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.
mp_rational: implement ipow_subs.
mp_integer: improvements in the ipow_subs() implementation.
mp_integer: a couple of fixes and improvements in the integral_cast tests.
math: add initial implementation of fp binomial coefficient.
math: improvements to the fp binomial implementation.

Now uses the logarithm of the gamma function.
math: rework the existing binomial specialisation to work with fp and arithmetic types
and use the new fp implementation.
mp_integer: extend the binomial implementation to negative bottom arguments
and overhaul the math::binomial() implementation to work the same way
math::pow() does for integral arguments.
mp_integer: minor test addition.