Add version of hws2xml built with mono

Playing Hammerwatch on a Mac, was playing with upgrades and accidentally discovered teleporters autosave.

This adds a build of hws2xml compiled with [Mono](http://www.mono-project.com/). This version runs fine on a Mac using Mono. Run it as `mono hws2xml-mono.exe example.hws example.xml`

I know next to nothing about Mono, but it doesn't seem possible to (easily) build HWSEdit with Mono:

    /usr/local/Cellar/mono/3.10.0/lib/mono/4.5/Microsoft.Common.targets: error : Tool exited with code: 1. Output: Error: Invalid ResX input.
    Position: Line 142, Column 5.
    Inner exception: An exception was thrown by the type initializer for System.Drawing.GDIPlus

and

    /usr/local/Cellar/mono/3.10.0/lib/mono/4.5/Microsoft.Common.targets: error : Tool exited with code: 1. Output: Error: Invalid ResX input.
    Position: Line 142, Column 5.
    Inner exception: An exception was thrown by the type initializer for System.Drawing.GDIPlus