Reorganize pipeline code into several submodules

README.md

lightmotif/benches/ecoli.rs

lightmotif/src/lib.rs

lightmotif/src/pli/mod.rs

lightmotif/src/pli/platform/avx2.rs

lightmotif/src/pli/platform/generic.rs

lightmotif/src/pli/platform/mod.rs

lightmotif/src/pli/platform/sse2.rs

lightmotif/src/pli/scores.rs

lightmotif/src/pli/vector.rs

lightmotif/src/seq.rs

lightmotif/tests/dna.rs