Fixes issue #13.

Replace ArrayList<Token> special_tokens with HashSet.
Merge pull request #12 from stepinto/master

Expose position information of type/method names
Merge pull request #14 from stepinto/fix-issue-13

Improve parser performance
Improve performance by not keeping all comment tokens in memory
Merge pull request #15 from stepinto/last-comment-token

Improve performance by not keeping all comment tokens in memory