Add clang-tidy -line-filter option to filter findings by line ranges.

Summary:
This is going to be used for a clang-tidy-diff script to display
warnings in changed lines only. The option uses JSON, as its value is not
intended to be entered manually.

Reviewers: klimek

Reviewed By: klimek

Subscribers: cfe-commits

Differential Revision: http://reviews.llvm.org/D3873