First pass at some prime number utils.

is_prime to check for a prime and a function to generate a list of primes.
A solution to problem 49 from project euler.

Still needs some polish and timing info. But it generates a correct
answer so checkpointing with a commit.
Actually use the sqrt when checking the prime.
Add timing information.
Add tests and a bug fix found by tests.

Since small numbers might have a sqrt == 2 add +1 to the range used for testing.
Add reversible related tools and tests.
Add check for leading zeroes.
Add a brute force solution.

It works on the small 1000 number test case but fails horribly on the
10 ** 9 case. Still worth saving before moving on.
A little more cleanup in figuring out leading zeroes.
Add a better solution for problem 145.
Add a function to check for circular primes.

Also add some tests for that function.
Add a solution for problem 35.