Add mypy config

The _version.py and testUSB1 modules are both ignored by mypy
since they're "internal" to the package. They can be included in the
future by simply removing their 'ignore_errors' lines.

Author: ahawker

mypy.ini

@@ -0,0 +1,9 @@
+[mypy]
+warn_return_any = True
+warn_unused_configs = True
+
+[mypy-usb1._version]
+ignore_errors = True
+
+[mypy-usb1.testUSB1]
+ignore_errors = True