MANTA-17 Reorganize core assembly routine into a separate library
MANTA-17 refine smallAssembler:

- Reorganize assembler interface to include constant input data (reads) and non-constant output (read info)
- Add contig id to each read to record which contig it was used in
- Remove qname from assembler -- this a detail the assembler ideally isn't be exposed to
- Put first simple assembler test in place
- make unused count more accurate, only the first matching word for each read can decrement the unused count, so that total unused == readCount
- don't count read as used if its contig is rejected because of min seed reads
- simplify "mode" functions to use a bool instead for forward/backward behavior
- change minSeedReads behavior to match documentation -- previously off by one. Adjust default min seed reads to keep behavior the same