python: make `import magnum.math` working.

src/python/magnum/__init__.py

@@ -27,6 +27,12 @@
 
 from ._magnum import *
 
+# This feels extremely hackish, but without that it wouldn't be possible to
+# do `import magnum.math`, which is weird (`from magnum import math` works,
+# tho, for whatever reason)
+import sys
+sys.modules['magnum.math'] = _magnum.math
+
 __all__ = [
     'Deg', 'Rad',