[clang-tidy] Move some of the misc checks to readability/

Summary:
Some of the misc checks belong to readability/. I'm moving them there
without changing check names for now. As the next step, I want to register some
of these checks in the google and llvm modules with suitable settings (e.g.
BracesAroundStatementsCheck). I'm not sure if we want to create a "readability"
module, probably not.

Reviewers: djasper

Reviewed By: djasper

Subscribers: curdeius, cfe-commits

Differential Revision: http://reviews.llvm.org/D5792