Add support for gclient fetcher, support for comments that appended to a line

1. gclient fetcher, which is be able to clone a google depot-tools-based project, such as chromium, gclient, etc.
2. enhance the parser of bitbake, it can parse parse the line that end up with a commit, like:
   ABC = "some#value"  # comments
   after the strip_comments(), the line will be striped to: ABC = "some#value".
*the README.md is not usefull, plz drop it.