Added primitive: window_type

  This will return a string such as "WINDOW_NORMAL", "WINDOW_DOCK",
 etc.

  This updates #3.
  Test against the window_type() too.

  This should avoid even fewer collisions.

  This updates #3.
  Split implementation into distinct files.

  All the Lua primitives are now defined in a dedicated file,
 `bindings.c` which forced a change to the storage-type and the
 `Makefile`.

  TODO:  Update Makefile to be cleaner.
Arrange lua primitives alphabetically
Added "make indent" target to format code.

Formatted code using the same.
  Clean indent-produced files, if present.
  Duplicate the config-filename to avoid a double-free.
  Added primitive "exists()", and use it.

  This just tests if the file/directory exists.
  Document readdir + exists
Compile our two sources separately.

This is neater and speeds up compilation.