Improved GMP wrapper extension

This extension wraps the mpz_() and mpf_() functions in libgmp. It differs from the delivered GMP extension in PHP in a few key ways:

• Object method API rather than function/resource based API
• Support for floating point numbers

API summary

In the API summaries below, the psuedo type Number represents an instance of GMPi, an int, a float (if appropriate), or a numeric string. Numeric strings may be expressed as decimal, binary (with a leading '0b'), hex (with a leading '0x'), or octal (with a leading '0').

interface GMPi {
  public function add(Number $val): GMPi;
  public function sub(Number $val): GMPi;
  public function mul(Number $val): GMPi;
  public function div(Number $val): GMPi;
  public function pow(Number $val): GMPi;
  public function cmp(Number $val): int; // -1, 0, 1
  public function neg(): GMPi;
  public function abs(): GMPi;
  public function toFloat(): GMPi\Float;
  public function toInteger(): GMPi\Intger;
  public function __toString(): string; // decimal output
  public function __debugInfo(): array; // 'dec' and 'hex' keys
}

namespace GMPi;
class Float implements \GMPi {
  public function __construct(Number $val, int $base = 0,
                              int $precision = ini_get('gmpi.precision'));
  public function toParts(): array; // 'mantissa' and 'exponent' keys
  public function toString(int $base = 10,
                           int $maxpad = ini_get('gmpi.padding'));
}

namesapce GMPi;
class Integer implements \GMPi {
  public function __construct(Number $val, int $base = 0);
  public function mod(Number $val): GMPi\Integer;
  public function and(Number $val): GMPi\Integer;
  public function or(Number $val): GMPi\Integer;
  public function xor(Number $val): GMPi\Integer;
  public function powMod(Number $val, int $mod): GMPi\Integer;
  public function congruent(Number $val, int $mod): GMPi\Integer;
  public function toString(int $base = 10): string;
}

Additionally, GMPi* implementations support similar operator overloading to the GMP object.

Invalid inputs of any type will throw an instance of \TypeError