Implemented clang-tidy-check-specific options.

Summary:
Each check can implement readOptions and storeOptions methods to read
and store custom options. Each check's options are stored in a local namespace
to avoid name collisions and provide some sort of context to the user.

Reviewers: bkramer, klimek

Reviewed By: klimek

Subscribers: cfe-commits

Differential Revision: http://reviews.llvm.org/D5296