Beta branch

[sfleischman105]

Updated pleco to 0.2.2 and pleco_engine to 0.0.3.

Changes this entails:

1. Added more functions to PlecoSearcher,including starting work on the UCI loop. More functions have been added allowing more control.
2. Clean up UCIOptions in pleco_searcher. Now, each option has a Boxed generator attached, which on change returns the closure to modify PlecoSearcher, alongside the value to modify it to.
3. Added failure create to better describe errors. For now, this is only used for generating Boards from fen strings.
4. Added a method to check fen strings for correctness, is_valid_fen().
5. Re-organization of engine files. that module is now deleted, and placed into tools for UCILimit and Searcher trait. Anything fen related goes into the new folder, board::fen.
6. Better documentation! <3 hyperlinks
7. More tests!

[coveralls]

Coverage decreased (-0.4%) to 81.886% when pulling e39f0b8 on Beta-Branch into 059b34d on master.

[coveralls]

Coverage increased (+0.8%) to 83.09% when pulling 233a9dc on Beta-Branch into 059b34d on master.