add homebrew installation

[MartinDelille]

I create a homebrew formula for qmlfmt for macOS user.

The formula won't be accepted yet in the homebrew core tap because it isn't popular enough yet: Homebrew/homebrew-core#41200 (comment)

The only problem I have is that the version is not displayed when I set it like in the .travis.yml file:

cmake .. -DQMLFMT_VERSION:STRING=1.0.85
-- The C compiler identification is AppleClang 9.0.0.9000039
-- The CXX compiler identification is AppleClang 9.0.0.9000039
-- Check for working C compiler: /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/cc
-- Check for working C compiler: /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/cc -- works
-- Detecting C compiler ABI info
-- Detecting C compiler ABI info - done
-- Detecting C compile features
-- Detecting C compile features - done
-- Check for working CXX compiler: /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/c++
-- Check for working CXX compiler: /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/c++ -- works
-- Detecting CXX compiler ABI info
-- Detecting CXX compiler ABI info - done
-- Detecting CXX compile features
-- Detecting CXX compile features - done
-- Configuring done
-- Generating done
CMake Warning:
  Manually-specified variables were not used by the project:

    QMLFMT_VERSION


-- Build files have been written to: /Users/martin/dev/clone/qmlfmt/build

[jesperhh]

Thanks for adding this!

The version number issue was mentioned in #17, and I haven't gotten around to fix it yet.

I don't know how homebrew "recipes" are normally handled - would it make more sense if you add everything to this repo, or is it usually done in a separate repo?

[MartinDelille]

No a tap repository need the homebrew- prefix like https://github.com/martindelille/homebrew-tap

You can either use my tap and I'll maintain it since I watch the repository.

You can also create your own tap but if you're not on macOS, it'll be harder to maintain.

[jesperhh]

I will just use yours then - can I merge the PR, or does it need anything else?

[jesperhh]

I take that as a "no further changes needed" and will merge it as-is

[MartinDelille]

Yes indeed: nothing more is needed!