Add misser lexer entry for nesC to languages.yml

The nesC entry in the languages.yml file was missing a lexer entry
and thus wasn't getting picked up. This adds the required lexer line.
Add R package ignores to vendor.yml

Ignore vignette and external data directories which contain no R source code
Merge branch 'master' into 814

Conflicts:
	lib/linguist/languages.yml
Change R package ignores to absolute paths
nesC
Merge pull request #1255 from github/680-update

680 update
Merge branch 'master' into 1042

Conflicts:
	lib/linguist/vendor.yml
Merge commit 'refs/pull/1042/head' of github.com:github/linguist into 1042

Conflicts:
	lib/linguist/vendor.yml
Merge pull request #1256 from github/1042-update

1042 update