Set up initial leiningens project structure.
Solutions to the first two problems.
Added .nrepl-port to the .gitignore file.

This is generated by by LightTable to store the port for the REPL connection, which definitely doesn't need to be in the repo.
Solved Problem 3.

My solution borrows heavily on a StackOverflow answer (http://stackoverflow.com/a/7625207) to the question of efficiently generating infinite sequences of primes.