added a `data` reader for accessing the full parsed data set

So in further testing and practice, I found it helpful to have the
`args` available separate from the `opts` for inspection and validation.
However it is still very useful to have a reader that combines them
in a way that is convenient for passing to a handler of some sort.

I went back to having `args` be the arguments and added a `data`
reader that combines the arguments with the trailing opts hash.
reworked HelpExit handling to not raise with opts explanation

In practice, its better to formally provide the opts explanation
as `to_s`.  The HelpExit handling is now the same of VersionExit.
changed the value option to show the up-cased option name as the value

This is in the explanation string.  Before it would put the default
value in there.  Its kinda confusing though in practice, b/c you
really just want a generic placeholder.