Explain that eqv doesn't work for arbitrary objects
Explain that eqv doesn't work for arbitrary objects

And add a note about how to implement `eqv` if one needs this behaviour.
This should address the issue raised in #81.

dnmfarrell/doc,antquinonez/doc,MadcapJake/doc,LLFourn/doc,LLFourn/doc,gfldex/doc,perl6/doc,stmuk/doc,perl6/doc,dmaestro/doc,gfldex/doc,MasterDuke17/doc,tbrowder/doc,dmaestro/doc,dha/doc,MadcapJake/doc,MasterDuke17/doc,dmaestro/doc,cygx/doc,dnmfarrell/doc,MasterDuke17/doc,stmuk/doc,jkeenan/doc,dnmfarrell/doc,cygx/doc,antquinonez/doc,gfldex/doc,jkeenan/doc,dha/doc,gfldex/doc,LLFourn/doc,dnmfarrell/doc,muraiki/doc,jonathanstowe/doc,jkeenan/doc,tbrowder/doc,perl6/doc,perl6/doc,dnmfarrell/doc,jonathanstowe/doc,stmuk/doc,antquinonez/doc,jkeenan/doc,MadcapJake/doc,dha/doc,MasterDuke17/doc,gfldex/doc,tbrowder/doc,cygx/doc,stmuk/doc,muraiki/doc,LLFourn/doc,dmaestro/doc,dha/doc,muraiki/doc,antquinonez/doc,dmaestro/doc,MadcapJake/doc,muraiki/doc,jkeenan/doc,perl6/doc,cygx/doc,MadcapJake/doc,jonathanstowe/doc,jonathanstowe/doc,tbrowder/doc,cygx/doc,jonathanstowe/doc,antquinonez/doc,stmuk/doc,muraiki/doc,LLFourn/doc,dha/doc