macOS homebrew package (was: Re: Survex 1.2.36 released)

[Olly Betts]

Thanks to Rob Jones you can now install Survex on macOS using the
Homebrew package manager, which provides an easier way to install a
recent version which we can keep in step with releases.  The disk
image hasn't been updated since 1.2.27 which is just over 2 years
old now.

If you don't already use Homebrew, you'll need to install that first.
Then to install Survex:

  brew update
  brew install https://survex.com/~olly/survex.rb

The first time you do this it may take a while as it has to install
all the dependencies first.  Subsequent updates should be faster.

This packaging is fairly new - if you hit any teething problems, please
report them to the bug tracker or mailing list. 

Cheers,
    Olly