Fixes https://github.com/gitlab4j/gitlab4j-api/issues/1058

* Added Encoding constant (#342).
* Mods to use Encoding enum constant (#342).
* Mods to support reading content from files when using CommitsApi.createCommit() (#342).

* Load forks of a project with Pager
* Load comments of a commit with Pager
* Load merge request changes
* Load merge request participants.
* Method to request repository contributors
* getMergeRequestChanges method needs list of diffs
* Fixed getFile method does not handle spaces in path correctly

* Add a variation of the getCommits() method that supports Paging and a path.  A simple variation to make it easy to find all commits for a given file.

* Added get commits by path method