Subzero: Doxygenify TODO comments.

Uses a nasty regexp to turn something like:

  // ... TODO(stichnot): Fix
  // this.

into:

  /// ... @todo TODO(stichnot): Fix
  /// this.

so that doxygen can generate the TODO list.

Matches "TODO:" and "TODO " and "TODO(...".

BUG= none
R=rkotlerimgtec@gmail.com

Review URL: https://codereview.chromium.org/1489413007 .