Experimental MEX version

Investigate the advantages and disadvantages of using the MEX interface instead of the Engine interface.

Benchmarking

engEvaluate["r=rand(1,50000000);"]
engGet["r"]; // AbsoluteTiming

• Engine gives 0.9 s.
• MEX with mexGetVariable() gives 0.73 s.
• MEX with mexGetVariablePtr() gives 0.52 s.