Add brew package

[leakec]

For MacOS users, a brew package would be a great way to install things so they don't need to worry about dependencies.

[leakec]

Notes

• To add a Python dependency see here
  • This didn't really work, and I decided users should likely install the package via pip anyway, that way this matches the deb and rpm installations.
• To add package dependencies see here (also, this just has the general way to build the formulae).
• See here for how to create a brew formula without a tarball.
• This whole thing will be packaged as a single *.rb file that users can download and install with brew install sihm.rb.
• This was used to take care of an empty installation issue.
  • Need to write something to the prefix location. Just writing an empty dummy file.

[leakec]

This is tested and works. I'm not sure tab completion files are being installed correctly, but willing to sort that out in another issue if need be.