signature() takes first parameter off of unbound methods

[epsy]

funcsigs.signature() treats unbound methods as any other method, despite m.self being None.

The attached pull requests adds a test case and fix. I've used a positional-only parameter because of this behaviour:

>>> class Test(object):
...     def method(self, *args, **kwargs):
...         return self, args, kwargs
...
>>> Test.method(Test())
(<__main__.Test object at 0x2c9fad0>, (), {})
>>> Test.method(self=Test())
Traceback (most recent call last):
  File "<input>", line 1, in <module>
TypeError: unbound method method() must be called with Test instance as first argument
 (got nothing instead)

[aliles]

Version 0.4 of funcsigs has been published to PyPI which includes epsy's fix for this issue.