mp_integer: some more notes and simplification/perf improvements
from the use of the view class.
mp_rational: document and test the (in)equality operators.
mp_rational: less-than operator.
mp_rational: finish the comparison operators.
mp_rational: integral exponentiation.
mp_rational: abs() and hash.
mp_integer: move the interoperable type detector outside the template.
mp_rational: minor test addition.
mp_integer: overhaul the pow() implementation to be more general, similarly to integer.
mp_rational: exponentiation.
mp_rational: implement print_tex_coefficient.
A couple of todo items for piranha.hpp and mp_rational.
mp_rational: implement math::negate().
mp_rational: implement sin/cos.
mp_integer: change the implementation of sin/cos to match mp_rational's.

Plus a minor test addition to mp_rational.
mp_rational: implement math::abs().
mp_integer: implement integral_cast.
mp_rational: partial,evaluate and subs implementation.
mp_rational: implement integral_cast.
mp_integer: implement ipow_subs.