Cmake support

[zkSNARK]

I realize that parson is small enough just to include directly into every project you want it in, but I thought I'd test anyway... so I made a basic Cmake script to build and install parson as a library using modern cmake techniques. It seems like it works pretty well, but the project directory structure has to be rearranged a bit.

The benefits are that you can use it within a find_package command so it is trivial to include in other projects that use Cmake.

Is this something you would be interested in?