To make use of krust's multithreaded cocurrency test fasta data with multiple records.

Run krust on the test data, searching for kmers of length 5, like this:

$ cargo run 5 cerevisae.pan_S288C_chrI.fa

or, searching for kmers of length 21 across multiple records:

$ cargo run 21 cerevisae.pan.fa

Branches are variations in implementation:

-- main uses rayon's parallel iterator by collecting the rust-bio fasta Reader into a vector

-- ParallelBridge uses rayon's ParallelBridge (https://docs.rs/rayon/1.5.1/rayon/iter/trait.ParallelBridge.html) (This seems to be slightly slower than collecting and using par_iter)

-- std_threads uses Rust's standard library thread to process in parallel

-- single_thread has no parallel processing