Searcher Switching

[ccjeremylo]

Summary of change:

• Moved all searcher related files/modules into a separate searcher folder/package
• Refactored the original Searcher class into a class hierarchy:
  • abstract base class = Searcher
  • MiniMaxVariant inherits from Searcher
  • NegaMaxSp inherits from MiniMaxVariant
  • NegaMaxLazySMP inherits from NegaMaxSp
• Most performance enhancing algorithms are refactored into private methods within the MiniMaxVariant class:
  • e.g. null move pruning, iterative deepening, aspiration windows, and quiescence
• Use factory pattern (SearcherFactory) to create/build concrete Searcher objects
• Refactored the MoveOrder logic as a separate abstract base class, independent from Searcher:
  • MvvLvaHeuristic inherits from MoveOrder
• Updated config settings
• Removed dodgy tests, should improve test methods for searchers in next change

Remarks:

• This is purely a code refactoring, to improve code extendibility and readability
• Expect no performance change
• Please refer to #10 for design heuristics/considerations
• The naming of functions is not ideal, naming suggestions are welcome
• A lot more code refactoring can be done, but aim to keep this PR shorter and simple (incremental changes) - any further refactoring recommendations are welcome

Successfully merging this PR should close #10.

[KYLChiu]

LVGTM on first round review, follows what we discussed in #10 closely. Think some minor changes and docstrings need to be added and should go through smoothly - thanks a lot!!