First version of a clang-rename tool.

Summary:
Note that this code is still grossly under-tested - the next steps will
be to add significantly better test coverage.

Patch by Matthew Plant.

Test Plan:

Reviewers:

Subscribers:

git-svn-id: https://llvm.org/svn/llvm-project/clang-tools-extra/trunk@215839 91177308-0d34-0410-b5e6-96231b3b80d8
Remove mention of non-existent 'test' directory.

git-svn-id: https://llvm.org/svn/llvm-project/clang-tools-extra/trunk@215840 91177308-0d34-0410-b5e6-96231b3b80d8
Fix link libraries for clang-rename.

git-svn-id: https://llvm.org/svn/llvm-project/clang-tools-extra/trunk@215843 91177308-0d34-0410-b5e6-96231b3b80d8