cpp11-migrate: Minor command-line fixes and improvements

* all transforms are in the same category
* all transforms' options are in the same category
* display the CommonOptionParser extra-help (which describe in more details the
  compilation database stuff)
* add EXAMPLES section

Author: Guillaume Papin <guillaume.papin@epitech.eu>


git-svn-id: https://llvm.org/svn/llvm-project/clang-tools-extra/trunk@185660 91177308-0d34-0410-b5e6-96231b3b80d8