Add support for inference of method arguments

This MR closes #409 (closed).

• A new test has been added to ensure that method arguments are inferred correctly, complementing the same functionality for functions
• A new function is provided, utils._infer_args_from_function_except_n_args to allow an arbitrary number of arguments to be ignored.
• utils.infer_parameters_from_function has been updated to infer if a passed argument is a function or a method (or will raise a ValueError if it is neither.

The behaviour of utils.infer_parameters_from_function may not be considered optimal, as it will fail in the case that an object with a __call__() method is passed as an argument. If you're keen for this form to be supported I can add an additional case for it.

bilby/core/utils.py

@@ -103,8 +103,8 @@ def _infer_args_from_function_except_n_args(func, n=1):
 
     Extended Summary
     ----------------
-    This function is intended to allow the handling of named arguments 
-    in both functions and methods; this is important, since the first 
+    This function is intended to allow the handling of named arguments
+    in both functions and methods; this is important, since the first
     argument of an instance method will be the instance.
 
     See Also