games/xray-16: Improved version of the X-Ray Engine, the game engine used in the world-famous S.T.A.L.K.E.R.

This port can be used for run S.T.A.L.K.E.R.

Supported game platforms:

• Clear Sky 1.5.10 (minor bugs are possible, but the game is stable finishable).
• Call of Pripyat 1.6.02.
• Call of Chernobyl 1.4.22.

Shadow of Chernobyl is not supported yet.
Legends of the Zone/Enhanced Edition is not supported and won't ever be
likely.

PR: 282815