grep: move match and diff logic to new module
commands.grep() has lots of functions and classes. Let's split it into
reusable components so we can leverage them to implement a revset predicate
for 'hg grep --diff'. I want to do 'hg log -r "diff(pattern)"'.
Mercurial
=========
Mercurial is a fast, easy to use, distributed revision control tool
for software developers.
Basic install::
$ make # see install targets
$ make install # do a system-wide install
$ hg debuginstall # sanity-check setup
$ hg # see help
Running without installing::
$ make local # build for inplace usage
$ ./hg --version # should show the latest version
See https://mercurial-scm.org/ for detailed installation
instructions, platform-specific notes, and Mercurial user information.