Add Rmpc_log10, Rmpc_mul2si and Rmpc-div_2si (new in 1.0.0)
Accommodate namechange of mpc_mul_2exp and mpc_div_2exp to mpc_mul_2ui and mpc_div_2ui (respectively) in mpc-1.0.0.
Rewrite the detecting of availability of double _Complex and long double _Complex types by looking for _Complex_I instead of _MPC_H_HAVE_COMPLEX (in line with the way mpc.h currently does it).