Tests:
   1*   initializations and to_s
   2*   basic integer arithmetics and coersion to Z
   3*   integer logical operators
   4*   comparisions between Z, Q, FixNum and BigNum
   5*   basic rational arithmetics and coersion to Q
   6    bit operations, scan0, scan1
   7*   exponentiation and exponentiation modulo
   8*   divide by zero exceptions
   9*   sgn, neg, abs
  10*   fibonacci, factorial, nextprime
  11*   swap
  12*   floor, ceil, truncate
  13*   to_i, to_d
  14*   shifts, last_bits
  15*   logical tests, roots
  16*   floating point init with and without explicit precision
  17*   basic floating point arithmetics and coersion to F
  18*   default_prec and default_prec=
  19*   integer division methods
  20    mpfr - exp and log
  21    mpfr - trigonometry
  22    mpfr - type tests
  23    mpfr - sqrt and power
  24*   jacobi, legendre, remove
  25*   gcd, gcdext, lcm, invert
TODO:
  gcd, lcm
  cmpabs
  integer and integer->rational division, modulo
  more number theoretic functions
  random numbers
  range errors
  mpz_size
  full coverage?