[clang-tidy] Refactor: Move misc clang-tidy checks to namespace clang::tidy::misc

[clang-tidy] Refactor: Move misc clang-tidy checks to namespace clang::tidy::misc

clang-tidy checks are organized into modules. This refactoring moves the misc
module checks into the namespace clang::tidy::misc

http://reviews.llvm.org/D7996

Patch by Richard Thomson!

llvm-svn: 230950