mpz/mpq should implement numbers.Integral/Rational

[skirpichev]

Right now, for example, numerator/denominator attributes are missing for mpz. Also, classes aren't properly registered.

In [6]: gmpy_cffi.mpz(2)
Out[6]: mpz(2)

In [7]: _6.numerator
---------------------------------------------------------------------------
AttributeError                            Traceback (most recent call last)
<ipython-input-7-e929b9596bbc> in <module>()
----> 1 _6.numerator

AttributeError: 'mpz' object has no attribute 'numerator'

In [8]: isinstance(_6, numbers.Integral)
Out[8]: False

In [9]: isinstance(gmpy_cffi.mpq(2), numbers.Rational)
Out[9]: False