Re-add boost dep

We use it anyway...
Remove primes-tmpl and primes-simple

Not that template metaprogramming isn't awesome, but that was kind of a
lame execution.
Add primeTable
Remove underscores from test cases

gtest is picky.
Remove prime-table.cc
ifndef guard
underscore -> camel case
primes.cc -> main.cc, rule for nth-prime
Shorter README