NEW: games/steamworks-nosteam

Hi,

This is a stub library based on the MIT-licensed source of
Steamworks.NET [1]. Steamworks.NET.dll ships with many games, some of
which are based on FNA. Its purpose is to serve as a C# wrapper for
the C++ API of the Steam client (which is proprietary). Since there is
no Steam client on OpenBSD, games that try to communicate with Steam
via Steamworks.NET crash because of missing API references.

This steamworks-nosteam port currently consists only of a stub
Steamworks.NET.dll that can serve as a drop-in replacement of the file
that comes bundled with games. Of note, it only stubs API calls; it
does NOT deal with anything DRM-related!

With this, the fnaify port can run the following additional FNA games,
on top of the ones that were supported before:

* Salt and Sanctuary
* Bleed 2
* Charlie Murder
* The Dishwasher: Vampire Smile
* Hidden in Plain Sight
* Hyphen
* Press X to Not Die
* Solaroids: Prologue

There are potential other future uses. An upcoming port of XnaToFna [2]
could make use of it as well. There are stubs for other commonly used
Steamworks wrappers (libCSteamworks.so, libSteamworksNative.so) that
might be candidates for addition in the future; therefore the port name
steamworks-nosteam.

ok?

[1] https://github.com/rlabrecque/Steamworks.NET
[2] https://github.com/0x0ade/XnaToFna