Improve Git Access Performance

[jimbethancourt]

RefactorFirst spends a significant portion of time performing Git access for codebases with a deep commit history. Speed this access up using multithreading.

[jimbethancourt]

Tests against the Jenkins codebase
20:22 - 0.8.0
17:58 - GitLogReader.fileLog() improvements
11:57 - GitLogReader.captureChangeCountByCommitTimestamp() improvements
11:48 - GitLogReader.captureChangeCountByCommitTimestamp() changes