Docs: Add taxonomy term variables to the list of vars.
Docs: Add taxonomy term variables to the list of vars.

Taxonomy Term pages have variables in addition to those on "node"
pages.  Documenting these variables with all the other node variables
makes them easier to find.

Fixes: #1155

mdhender/hugo,melo/hugo,fedelibre/hugo,ifraixedes/hugo,digitalcraftsman/hugo,gohugoio/hugo,halostatue/hugo,fedelibre/hugo,ryanclarke/hugo,fedelibre/hugo,derekperkins/hugo,coderzh/hugo,mdhender/hugo,fhergomez/hugo,abourget/hugo,tjyang/hugo,anthonyfok/hugo,mdhender/hugo,digitalcraftsman/hugo,tjyang/hugo,vbatoufflet/hugo,mdhender/hugo,jygastaud/hugo,MarkDBlackwell/hugo,tatsushid/hugo,mayah/hugo,badoet/hugo,kujohn/hugo,gohugoio/hugo,jygastaud/hugo,Zenithar/hugo,anthonyfok/hugo,fhergomez/hugo,tubo028/hugo,tatsushid/hugo,badoet/hugo,ffrizzo/hugo,soundrussian/hugo,halostatue/hugo,bramp/hugo,ffrizzo/hugo,ryanclarke/hugo,sprig/hugo,ifraixedes/hugo,mitchchn/hugo,bogem/hugo,soundrussian/hugo,anthonyfok/hugo,tischda/hugo,tubo028/hugo,tischda/hugo,kujohn/hugo,melo/hugo,MarkDBlackwell/hugo,bramp/hugo,vbatoufflet/hugo,mayah/hugo,gohugoio/hugo,mitchchn/hugo,Zenithar/hugo,coderzh/hugo,derekperkins/hugo,bogem/hugo,fedelibre/hugo,sprig/hugo,abourget/hugo