upgrade: split actual upgrade code away from the main module
The main module is getting big and hard to follow. So we are splitting all the
logic to actually run an upgrade in a sub module. It nicely highlight that there
are very few actual call point to the code we just moved.
Differential Revision: https://phab.mercurial-scm.org/D9476
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.