Convert pybigtools to a mixed Rust/Python project to ensure that sour…

…ce builds with pip behave correctly

pybigtools/pybigtools/__init__.py

@@ -0,0 +1,7 @@
+# This is here to make sure that source installs with pip work correctly
+
+from .pybigtools import *
+
+__doc__ = pybigtools.__doc__
+if hasattr(pybigtools, "__all__"):
+    __all__ = pybigtools.__all__