Add clojure prime finder
Aborted attempt to filter in parallel with reducer

can't do an infinite sequence of prime; have to cheat and specify a
maximum of numbers to check

Get almost exactly the same time to run as the non-parallel version: 342
msecs
Revert "Aborted attempt to filter in parallel with reducer"

This reverts commit defb16142068056dc28df3414faf563ac99e39f1.
Whoops, remove some reducer code that crept into the standard way of
doing this
Reimplement filter in terms of lazy-seq

Runs at or about the same speed
Keep and store only already-detected primes

This actually runs slower, around 410-425 msecs, maybe the cost of
many sqrts
Yes indeed it was the sqrt function - now faster

Now that we do the sqrt only once for each number to be tested
Fix bug - was leaving out 2 from final result