cpp11-migrate: Fixing doxygen warnings

For some reason doxygen doesn't seem to like the using namespace
clang::tooling in the source file and complaints about missing class
members.

Also fixed missing parameter documentation for TransformName in
SourceOverrides::applyReplacements().

Differential Revision: http://llvm-reviews.chandlerc.com/D1400

llvm-svn: 188394