Changefeed docs.
Updates to changefeed docs.
Added args.md
changed -> to &rarr;
Style changes to args.md
Added document to args.md.
Ported `r.args` to other languages.
Added args.md for Python and JS.
Ported changes to all three languages.
Fixed js changes.md
Fixed languages for changes.
Fixed changes header.
Fixed JS comments.
Added io to JS changes.md
Merge branch 'mlucy_changefeed_docs' into v1.13