Added more methods to Natural

Methods and operators added:
* random()
* and
* comparison
* bool
* in-place right shift
* size_in_bits()
* str
* is_even()
* is_odd()
Miller-Rabin test
Add is_perfect_square method to Natural
Simplify GMP code with _as_parameter_
Added more methods to Natural.

Methods and operators added are:
* jacobi_symbol()
* multiplication
* simple exponentiation
* right shift
Change Math.Numbers.Natural into Integer
Add Lucas primality test
Added script to plot Miller-Rabin error probability
Add or operator to Integer
Added generate_probable_prime function
Added plot for bit sizes 160..512
generate_probable_prime can generate 160-bit primes
Add is_divisible_by_ulong method to Integer
Optimize prime generation with sieve
Optimize prime generation (Lucas test)
Show MR probability also for bits=100
More complete set of tests for Math.Number
Additional optimizations for prime generation.
Revisited tests, docs and added generate_probable_safe_prime
Added Integer.inverse method