Add a small (naive?) impl of the Sieve of Eratosthenes on libshared
Use an enum to make the algorithm more self-descriptive
Avoid checking against even numbers, and limit the search to √candidate
Accept RUSTFLAGS on the Makefile
New sieve, based on the one on ruby
Add a max segment size, to avoid gigantic allocations
Change the solution to 07 to be based on the sieve
Also move 10 to the sieve (and get a 10x perf improvement)