[ADAM-431] Several random cleanups:

- README tweak

- wrap some long lines

- clarify command parsing in ADAMMain

- quote bash var

- make `GenomicRegionPartitioner` a case class

  seems like it’s well-suited to be one:
  - public ctor vals
  - boilerplate .equals method
  - wrapper ctor that uses companion object method can go into companion
    object

- remove no-op `remapContig` function

  the “NB” comment about it being a no-op seems to be correct, afaict
Merge pull request #431 from ryan-williams/tweaks

[ADAM-431] Several random tweaks: