grep: extract main search loop as searcher method
Still displayer part is in commands.grep(), the core grep logic is now
reusable. I'll revisit the displayer stuff later since it will be another
long series.
Mercurial
=========
Mercurial is a fast, easy to use, distributed revision control tool
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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
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See https://mercurial-scm.org/ for detailed installation
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