Update help output

Update help output

Various changes to console help output (and some to man output) based on
feedback in #1687:
 - People seem to prefer a centered startup header with some ASCII art,
   so made the first output line just like that (except if running with
   -quiet), and center the list of authors.
 - Always start the option description at a new line.
 - Give more space to various parts of the option list so that they are
   more likely to align up.
 - Split the file listing based on input/output type.  This causes,
   e.g., some logically related options (e.g., -cpi and -cpo) to get
   separated in the output, but this seems to be the preferred approach.
 - Add formatting to the synopsis on man pages (similar to how the
   options appeared in the 4.6-era man pages, except that reasonable
   line wrapping is still there).

Clean up the design for formatting the options list; now the actual
formatting code is better encapsulated in HelpWriterContext.

The user-visible scope of this change is limited to changing behavior
that changed between 4.6 and 5.0.  Thus, the changes here should be
sufficient to close #1687.

Change-Id: I349fd9021472f064f5797441090a3f3864868280