[#34] Show analysis result as a comment

Introduced two notifiers
- GithubCommitStatus - publishes analsis results as a commit status on GH
- GithubComment - publishes results as a regular comment

The GithubComment methods was added to workaround github which
shows only the most recent commit status. It means that when
both Travis-ci (or anything else) and Lint are connected to a repo there
will be a race condition where only one status provider wins.

A comment is not that fancy as a commit status but still providers
the most useful info.