bindTexture, renaming, rearrangement, fixes

- Drop the __ from header guards since those are reserved by the standard
  C/C++ libraries.
- Rename PyVideoScreen to PyDoom_Screen since the Py* naming convention is taken
  by Python. Use PyDoom_ as our internal prefix from now on.
- Implement Screen.bindTexture to upload textures to the given OpenGL context.
- Move the Type and Methods into statics inside Screen's C++ class.
- Disable screensaver/power-saving mode when PyDoom is running.
- Search for "PyDoom.zip" specifically, not just a zip with our program name,
  and /guarantee/ that it's null-terminated. If we can't feasably find it in our
  path, quit with an error code.