Improve Arithmetic

[billhails]

• General overhaul.
• move to libgmp?
• trig functions.
• Pre-compute constant values at compile time.
• allow numeric (not symbolic) arithmetic expressions in patterns.
• allow unpacking of numerator and denominator variables in patterns.
  • special case: a / b because there is a canonical form (via gcd).
  • match would fail if the actual argument is not integer or rational.
  • b would be bound to 1 if the argument was an integer.
  • can't allow arbitrary ops and combinations because i.e. (a + 2) * b
    can't uniquely determine a and b, and a ** 2 would require a
    to be bound to the square root of the actual argument.
• allow unpacking of the real and imaginary parts of a complex number in patterns.
  • another special case: a + b, b would be bound to 0i if the actual
    argument is not complex.