Update os.nim

added file/dirExists synonyms for existsFile/dir
Define $ operator for TRune
Define $ operator for TRune
Add info about twitter and bootstrapping from github to website.
Rename C sources dir to c_code.
added test cases from strange loop event
bugfix: doc generation for actors.nim works again
Merge pull request #779 from brihat/master

Define $ operator for TRune
Merge pull request #777 from fowlmouth/patch-4

Update os.nim