pys available in gmp.h, either as library functions or
     inlines, with the availability of library functions instantiated in the
     generated gmp.h at build time.
<li> <code>mpz_set_str</code> etc variants taking string lengths rather than
     null-terminators.
<li> <code>mpz_andn</code>, <code>mpz_iorn</code>, <code>mpz_nand</code>,
     <code>mpz_nior</code>, <code>mpz_xnor</code> might be useful additions,
     if they could share code with the current such functions (which should be
     possible)