[clang-tidy] Add new IdentifierNaming check

This check will try to enforce coding guidelines on the identifiers naming.
It supports lower_case, UPPER_CASE, camelBack and CamelCase casing and
tries to convert from one to another if a mismatch is detected.

It also supports a fixed prefix and suffix that will be prepended or appended
to the identifiers, regardless of the casing.

Many configuration options are available, in order to be able to create
different rules for different kind of identifier. In general, the
rules are falling back to a more generic rule if the specific case is not
configured.

http://reviews.llvm.org/D10933

Patch by Beren Minor!

llvm-svn: 245429