[clang-tidy] readability-identifier-naming - support for other case types

Added Camel_Snake_Case and camel_Snake_Back

class Camel_Snake_Case_Class_Name
{
  void private_Camel_Snake_Back_Method_Name();
}

Patch by James Reynolds!

Reviewers: alexfh

Subscribers: cfe-commits

Differential Revision: https://reviews.llvm.org/D21472

llvm-svn: 276110