std: Change CharEq to take `&mut self`
std: Change CharEq to take `&mut self`

This is similar to the previous commits to allow invocation of a closure through
a `&mut self` pointer because `&self` is disallowed. One of the primary
implementors of the CharEq trait is a closure type, which would not work if the
method continued to have `&self`.

In addition to changing mutability of the `matches` method, this modifies the
following methods from &CharEq to take a type which implements CharEq by value.

* trim_chars
* trim_left_chars
* trim_right_chars

Where these methods were previously invoked via

    s.trim_chars(&'a')

it would now be invoked through

    s.trim_chars('a')

[breaking-change]

philyoon/rust,vhbit/rust,rprichard/rust,jbclements/rust,zubron/rust,nwin/rust,jbclements/rust,pshc/rust,victorvde/rust,richo/rust,sae-bom/rust,nham/rust,pczarn/rust,philyoon/rust,pelmers/rust,mdinger/rust,defuz/rust,andars/rust,P1start/rust,aturon/rust,dwillmer/rust,gifnksm/rust,emk/rust,jashank/rust,waynenilsen/rand,aidancully/rust,AerialX/rust-rt-minimal,untitaker/rust,shepmaster/rand,nwin/rust,stepancheg/rust-ide-rust,richo/rust,omasanori/rust,dwillmer/rust,mvdnes/rust,krzysz00/rust,Ryman/rust,aidancully/rust,jashank/rust,nwin/rust,vhbit/rust,avdi/rust,aturon/rust,gifnksm/rust,dwillmer/rust,barosl/rust,kwantam/rust,dinfuehr/rust,mdinger/rust,ktossell/rust,retep998/rand,GBGamer/rust,defuz/rust,richo/rust,gifnksm/rust,krzysz00/rust,0x73/rust,avdi/rust,jbclements/rust,vhbit/rust,andars/rust,omasanori/rust,quornian/rust,quornian/rust,cllns/rust,andars/rust,kwantam/rust,GBGamer/rust,servo/rust,TheNeikos/rust,omasanori/rust,TheNeikos/rust,victorvde/rust,ktossell/rust,ejjeong/rust,gifnksm/rust,carols10cents/rust,aepsil0n/rust,quornian/rust,graydon/rust,jashank/rust,reem/rust,pelmers/rust,XMPPwocky/rust,mihneadb/rust,zubron/rust,rohitjoshi/rust,mihneadb/rust,Ryman/rust,XMPPwocky/rust,aturon/rust,seanrivera/rust,mihneadb/rust,emk/rust,nham/rust,servo/rust,reem/rust,hauleth/rust,mahkoh/rust,stepancheg/rust-ide-rust,pshc/rust,cllns/rust,vhbit/rust,pelmers/rust,philyoon/rust,rprichard/rust,bombless/rust-docs-chinese,ruud-v-a/rust,pelmers/rust,pczarn/rust,andars/rust,ebfull/rust,reem/rust,GBGamer/rust,AerialX/rust,jroesch/rust,ebfull/rust,AerialX/rust,bombless/rust,AerialX/rust,gifnksm/rust,aneeshusa/rust,untitaker/rust,KokaKiwi/rust,pshc/rust,rohitjoshi/rust,ejjeong/rust,Ryman/rust,dinfuehr/rust,0x73/rust,bombless/rust,richo/rust,pczarn/rust,servo/rust,ebfull/rust,zaeleus/rust,graydon/rust,avdi/rust,graydon/rust,untitaker/rust,dinfuehr/rust,victorvde/rust,miniupnp/rust,reem/rust,kimroen/rust,AerialX/rust-rt-minimal,bombless/rust,defuz/rust,KokaKiwi/rust,l0kod/rust,aepsil0n/rust,kimroen/rust,P1start/rust,GBGamer/rust,pczarn/rust,ebfull/rust,ktossell/rust,pczarn/rust,l0kod/rust,ejjeong/rust,rohitjoshi/rust,aneeshusa/rust,robertg/rust,dwillmer/rust,XMPPwocky/rust,robertg/rust,richo/rust,P1start/rust,aidancully/rust,pshc/rust,nwin/rust,hauleth/rust,XMPPwocky/rust,P1start/rust,avdi/rust,jbclements/rust,emk/rust,rohitjoshi/rust,TheNeikos/rust,krzysz00/rust,cllns/rust,pshc/rust,GBGamer/rust,quornian/rust,ruud-v-a/rust,rprichard/rust,GBGamer/rust,erickt/rust,nwin/rust,nham/rust,mdinger/rust,dwillmer/rust,aturon/rust,zaeleus/rust,stepancheg/rust-ide-rust,KokaKiwi/rust,AerialX/rust,l0kod/rust,erickt/rust,pshc/rust,ejjeong/rust,l0kod/rust,ebfull/rust,l0kod/rust,dwillmer/rust,ktossell/rust,P1start/rust,jroesch/rust,nwin/rust,hauleth/rust,0x73/rust,pshc/rust,kwantam/rust,GBGamer/rust,miniupnp/rust,untitaker/rust,victorvde/rust,servo/rust,aidancully/rust,emk/rust,krzysz00/rust,mvdnes/rust,l0kod/rust,zachwick/rust,zubron/rust,vhbit/rust,kwantam/rust,KokaKiwi/rust,bombless/rust,bhickey/rand,hauleth/rust,nwin/rust,erickt/rust,cllns/rust,sae-bom/rust,miniupnp/rust,nwin/rust,zachwick/rust,Ryman/rust,robertg/rust,andars/rust,emk/rust,0x73/rust,jashank/rust,sae-bom/rust,defuz/rust,graydon/rust,XMPPwocky/rust,defuz/rust,aidancully/rust,Ryman/rust,0x73/rust,ruud-v-a/rust,nham/rust,0x73/rust,jroesch/rust,rprichard/rust,rprichard/rust,servo/rust,carols10cents/rust,pshc/rust,arthurprs/rand,ruud-v-a/rust,reem/rust,zaeleus/rust,ruud-v-a/rust,kwantam/rust,P1start/rust,mahkoh/rust,emk/rust,pelmers/rust,aepsil0n/rust,victorvde/rust,omasanori/rust,jashank/rust,hauleth/rust,jbclements/rust,ejjeong/rust,mihneadb/rust,Ryman/rust,mahkoh/rust,stepancheg/rust-ide-rust,bombless/rust,seanrivera/rust,nham/rust,AerialX/rust-rt-minimal,defuz/rust,barosl/rust,graydon/rust,mvdnes/rust,robertg/rust,stepancheg/rust-ide-rust,zachwick/rust,KokaKiwi/rust,miniupnp/rust,cllns/rust,robertg/rust,sae-bom/rust,mahkoh/rust,stepancheg/rust-ide-rust,mihneadb/rust,quornian/rust,servo/rust,kimroen/rust,victorvde/rust,aepsil0n/rust,aneeshusa/rust,andars/rust,zubron/rust,barosl/rust,miniupnp/rust,erickt/rust,barosl/rust,jroesch/rust,bluss/rand,TheNeikos/rust,erickt/rust,kwantam/rust,sae-bom/rust,seanrivera/rust,erickt/rust,l0kod/rust,AerialX/rust-rt-minimal,mahkoh/rust,AerialX/rust,miniupnp/rust,quornian/rust,stepancheg/rust-ide-rust,jashank/rust,vhbit/rust,XMPPwocky/rust,dinfuehr/rust,jbclements/rust,mdinger/rust,gifnksm/rust,bombless/rust,reem/rust,Ryman/rust,jbclements/rust,rohitjoshi/rust,mdinger/rust,avdi/rust,aepsil0n/rust,aneeshusa/rust,untitaker/rust,krzysz00/rust,rprichard/rust,jbclements/rust,carols10cents/rust,zaeleus/rust,avdi/rust,l0kod/rust,philyoon/rust,rohitjoshi/rust,carols10cents/rust,hauleth/rust,nham/rust,GrahamDennis/rand,kimroen/rust,zaeleus/rust,dwillmer/rust,zachwick/rust,ktossell/rust,ejjeong/rust,erickt/rust,jashank/rust,aturon/rust,graydon/rust,vhbit/rust,ktossell/rust,zachwick/rust,mdinger/rust,aneeshusa/rust,aturon/rust,sae-bom/rust,AerialX/rust-rt-minimal,TheNeikos/rust,mihneadb/rust,achanda/rand,AerialX/rust-rt-minimal,huonw/rand,AerialX/rust,vhbit/rust,zubron/rust,carols10cents/rust,barosl/rust,pczarn/rust,miniupnp/rust,mvdnes/rust,dinfuehr/rust,barosl/rust,zaeleus/rust,jroesch/rust,robertg/rust,TheNeikos/rust,kimroen/rust,miniupnp/rust,carols10cents/rust,jbclements/rust,KokaKiwi/rust,aepsil0n/rust,GBGamer/rust,seanrivera/rust,aidancully/rust,ebfull/rand,servo/rust,kimroen/rust,zubron/rust,ktossell/rust,ebfull/rust,mahkoh/rust,richo/rust,kimroen/rust,P1start/rust,seanrivera/rust,jroesch/rust,philyoon/rust,omasanori/rust,jashank/rust,cllns/rust,krzysz00/rust,pelmers/rust,omasanori/rust,untitaker/rust,barosl/rust,zubron/rust,nham/rust,0x73/rust,emk/rust,philyoon/rust,jroesch/rust,jroesch/rust,dinfuehr/rust,quornian/rust,mvdnes/rust,ruud-v-a/rust,seanrivera/rust,zachwick/rust,dwillmer/rust,pczarn/rust,aneeshusa/rust,aturon/rust,zubron/rust,mvdnes/rust