Add a tween class for fading an element's alpha. Use it to fade our HUD in and out.
Add a tween class for fading an element's alpha. Use it to fade our HUD in and out.

csmalin/vimium,mrmr1993/vimium,llimllib/vimium,shaung/vimium,philc/vimium,hhsue/vimium,gdh1995/vimium,smblott-github/vimium,VPashkov/vimium,justalittlenoob/vimium,dimatter/vimium,bkudria/vimium,philc/vimium,justalittlenoob/vimium,decaffeinate-examples/vimium,dimatter/vimium,wildeyes/vimium,VPashkov/vimium,poacher2k/vimium,Aleroniponi/vimium,zhangmin510/vimium,poacher2k/vimium,douglas-larocca/vimium,csmalin/vimium,douglas-larocca/vimium,PickRelated/vimium,Lw-Cui/vimium,PickRelated/vimium,cyrixhero/vimium,hhsue/vimium,willsALMANJ/vimium,borgified/vimium,wildeyes/vimium,PickRelated/vimium,gdh1995/vimium,justalittlenoob/vimium,smblott-github/vimium-smblott,zhangmin510/vimium,csmalin/vimium,jb55/vimium-plus,mrmr1993/vimium,decaffeinate-examples/vimium,poacher2k/vimium,Robinson10240/vimium,crazypenguincode/vimium,Robinson10240/vimium,smblott-github/vimium,smblott-github/vimium-smblott,PrestanceDesign/vimium,tuchangwei/vimium,hhsue/vimium,Aleroniponi/vimium,Lw-Cui/vimium,cyrixhero/vimium,elderbas/vimium,PrestanceDesign/vimium,borgified/vimium,elegantwww/vimium,elegantwww/vimium,willsALMANJ/vimium,Aleroniponi/vimium,douglas-larocca/vimium,mrmr1993/vimium,crazypenguincode/vimium,dimatter/vimium,philc/vimium,gdh1995/vimium,jb55/vimium-plus,elegantwww/vimium,Lw-Cui/vimium,bkudria/vimium,willsALMANJ/vimium,elderbas/vimium,wildeyes/vimium,Robinson10240/vimium,VPashkov/vimium,cyrixhero/vimium,decaffeinate-examples/vimium,bkudria/vimium,tuchangwei/vimium,tuchangwei/vimium,zhangmin510/vimium,PrestanceDesign/vimium,borgified/vimium,elderbas/vimium,smblott-github/vimium