v1.6.0

Feature

• Add static method Int::random().
• Add static method Int::log().
• Add method Int::is_prime().
• Add method Int::next_prime().

Performance

• Optimized basic operations and many functions for Int.

Fixed

• Fix Int::pow(): (-1)^(-1) => -1

Change

• Make Int::sqrt(), Int::pow() static.
• Split pow(base, exp, module) -> pow(base, exp) & pow_mod(base, exp, module).

Misc

• More tests.
• More docs.