[pgpointcloud] Homebrew formula

[Pete Gadomski]

All,

I've created a head-only Homebrew formula for pgpointcloud:
https://github.com/gadomski/homebrew-headonly/tree/new/pgpointcloud

Homebrew (http://brew.sh) is a (widely used) package manager for OSX.
Packages are described by and installed from formula, which are simple
Ruby scripts.

Since pgpointcloud's cmake support was added after the v0.1.0 tag, for
now I've created the pgpointcloud formula as 'head only', so it can only
be used to install pgpointcloud from the `master` branch on Github. I
did not create the formula for the main Homebrew repository because
Homebrew has a policy to not accept any 'head only' formula. If
pgpointcloud got a new tag (v0.2.0?), I could submit my formula to the
main Homebrew repository instead, which would make the formula a bit
more findable.

I've included the option to build pgpointcloud with libght, though that
option is disabled by default (it can be enabled with a `brew install
pgpointcloud --with-libght`). The libght dependency is currently in pull
request on the main Homebrew repository
(https://github.com/Homebrew/homebrew/pull/29244), so I will wait until
libght is accepted before submitting pgpointcloud's formulae to
homebrew-headonly.

Any comments, suggestions, or changes to either branch are encouraged.
Again those links are:

- pgpointcloud: https://github.com/gadomski/homebrew-headonly/tree/new/pgpointcloud
- libght: https://github.com/Homebrew/homebrew/pull/29244

Cheers,
Pete

-- 
Pete Gadomski
Physical Scientist
Cold Regions Research & Engineering Lab
pete.gadomski at gmail.com
530.440.4630