Use inspect.signature() on Python 3

[vstinner]

The inspect.getargspec() function has been deprecated in Python 3:
https://docs.python.org/3/library/inspect.html#inspect.getargspec

[coveralls]

Coverage remained the same at 94.753% when pulling 638236d on haypo:signature into c9ac1d9 on stefankoegl:master.

[stefankoegl]

Thanks for your contribution! The Jenkins tests failed for Python 3.2 and pypy3. Can you please have a look and adapt your PR? Thanks :)

[vstinner]

Oh, I didn't know that you support Python 3.2. More and more projects are dropping Python 3.2 support. But right, PyPy only officially support Python 3.2 (even if they are actively working on Python 3.5 support).

Anyway, I fixed my change (I fixed the check on the Python version).

[coveralls]

Coverage remained the same at 94.753% when pulling d6e9a00 on haypo:signature into c9ac1d9 on stefankoegl:master.

[stefankoegl]

Nice, thanks :)

[vstinner]

Thanks.