add ntheory interface
add is_prime and next_prime
add gcd
ntheory python3 compat
add lcm
add gcdext
add invert
cleanup ntheory typechecking
add jacobi, legendre, kronecker
add fac
add bincoef, fib, fib2
cleanup ntheory typechecking
add lucas and lucas2
ntheory pep8 fixups
add missing ntheory tests