Upgrade MPC to version 1.0 (#13290) needs review

[Jeroen Demeyer]

Currently, Sage uses a development version of MPC (stable 0.9 had build
issues on certain platforms).

We should upgrade to the just-released MPC-1.0. While we're at it,
import MPComplexField by default and add MPC to the reference manual.

Please review:
http://trac.sagemath.org/sage_trac/ticket/13290

Thanks,
Jeroen.