This patch changes it so that `inspect.signature` is used instead of`inspect.getfullargspec` to get a function's signature, when using Python 3.Python 3.3 introduced the `inspect.signature` function as a new way to get thesignature of a function (as an alternative to `inspect.getargspec` and`inspect.getfullargspec`).  `inspect.signature` has the advantage that itpreserves the signature of a decorated function if `functools.wraps` is used todecorated the wrapper function.  Having a function's signature available is veryhepful, especially when testing things out in a REPL.

Instead of referencing parameter kinds as class attributes on the private`_ParameterKind` class we reference them on the public `Parameter` class.  Thishas two advantages:1) We don't use a private interface.2) The class attributes on `_ParameterKind` have only been added in Python 3.5,   but on `Parameter` they have existed since Python 3.3.

Some built-in functions (e.g. `map`) can't be inspected with`inspect.getargspec`, `inspect.getfullargspec` or `inspect.signature`.  Theexceptions from `inspect.getargspec` and `inspect.getfullargspec` are all caughtin the code, but `inspect.signature` raises a `ValueError` instead of a`TypeError`.  This exception is now also caught.