Improved help.

* Broke help into information, input, and output sections.
* Updated option argument placeholders to indicate types.
* Added quotes when referring to syntax.
* Simplified defaulting of '--scores-column' and '--labels-column'.
  Moved same column check to after setting defaults.
* Revised descriptions of '--scores-column' and '--labels-column'
  including simplified defaults.
* Added uppercase to report names to ease reading.
Added bounds check for column indices.