clang-format: do not reflow bullet lists

Summary:
This patch prevents reflowing bullet lists in block comments.

It handles all lists supported by doxygen and markdown, e.g. bullet
lists starting with '-', '*', '+', as well as numbered lists starting
with -# or a number followed by a dot.

Reviewers: krasimir

Reviewed By: krasimir

Subscribers: djasper, klimek, cfe-commits

Differential Revision: https://reviews.llvm.org/D33285

llvm-svn: 303556