Platform in review reports

• it now shows the tested platform when posting nixpkgs-review reports
  to github
• it now requires nixFlakes

Restore building unfree software

Since 2.4.1 we no longer were building unfree software because of the meta check.

Don't build what is broken

Previously our meta checks where broken, which lead to packages marked as broken to be built.

Now with comments

There is a new subcommand that will print the latest comments/reviews on
a pr in the console:

If you are in a review shell:

$ nix-review pr 17

You can get the comments with:

$ nix-review comments

This assumes that you have a github token set.

Minor fixes

• fix local evaluation when only packages are removed
• use attribute path when printing diffs between master and PR

Improved GitHub support

Nixpkgs-review can now merge and approve pull requests (See
merge and approve subcommand).
It can also post review results as comments on the pull request
(See post-result subcommand).

Github++

Added post-result/merge/approve subcommands

Github comments

Thanks to @bhipple nixpkgs-review can now post its report to the corresponding github issue.

Fixing evaluation of disabled python packages

• now print more update stats when locally evaluating
• fix evaluation of disabled python packages

Project rename

• rename to nixpkgs-review from nix-review
• switch to relaxed sandbox: d2e3fba
• no longer override nix's max-jobs option: 2bbdf97