New functions to implement:

- mpfr_mul_mpz, mpfr_div_mpz

Miscellaneous:

- implement a C++ wrapper [see with Torbjo"rn and/or Fabrice]

- for all instructions that call malloc/realloc/etc, handle error cases
  (for example return an int indicating if an error occurred)

- in all functions that do rounding, return an int indicating if the result
  is exact (i.e. no bit was lost) or not (like in mpfr_div_ui)

- detect overflow/underflow in exponent (from Ben Hinkle <bhinkle4@juno.com>)

- specify exponent size (suggestion from Ben Hinkle <bhinkle4@juno.com>)

- get rid of <math.h> whenever possible

- add mpfr_get_ld for 'long double' [asked by J-C Fauge`re] ?
  (exists since K&R, but has not necessarily a greater precision than double)
  cf http://anubis.dkuug.dk/jtc1/sc22/wg14/www/docs/n869/