Cleanup
Documentation: Added description for EntityDatabase

Courtesy of danij.
Relocated m_stack to libdeng1

Also spruced up the implementation a little.
Merge branch 'master' into mapdata-c++
Removed the global bspLeafs array

The GameMap is the correct way to access map data.
Removed global bspNodes and hedges arrays

These are not needed any more.
Removed the global lineDefs and sectors arrays

Not needed any more.
Removed global sideDefs, vertexes, and polyObjs arrays

Not needed any more. Now all map data is accessed via GameMap.