r320: - Add table of valid mode names and descriptions
r320: - Add table of valid mode names and descriptions

- Add helper function to look up mode by walking mode table

- Add parameter descriptions and option comments to options table

- Remove parameter count from options table and calculate it by walking
the parameter descriptions.  Remove explicit test for parameter count
exceeding MAXPARAMS; the compiler will warn about too many initializers
if this happens

- Reduce MAXPARAMS to the smallest we need right now

- Auto-generate usage messages from mode and options tables.  Provide
per-subcommand usage messages and subcommand list.

- Add curmode global for the use of PARSE_ERROR() macro

cmusatyalab/openisr,cmusatyalab/openisr,cmusatyalab/openisr,cmusatyalab/openisr,cmusatyalab/openisr