lot of changes: 
to CodePoster adds method postComment() which posts comment for given gist.
Also remo.v.e.s credentials from the source code of the CodePoster.java. Now they can be read from the environment variables.
adds to CodePoster main() with test "run" of the code.
TODO: still need to decide on format of CodePostCompleteEvent so that it can be used both for notifying on CodePost completion and comment code completion.