First release - all gist related methods.

All of the methods which are related to gist are implemented.

• delete comment
• delete gist
• fork gist
• get comment
• get gist
• get gist revision
• gist is starred
• list all gists
• list gist comments
• list gist commits
• list gist forks
• list starred gists
• list user gists
• post comment
• post gist
• star gist
• unstar gist
• update comment
• update gist