For optional parameter/choices, generate an overloaded config method
that takes no arguments. This makes it possible to convert from a bare
argument to one that takes an optional parameter without breaking
binary compatibility.
Changing from bool requiring true to string requiring the empty string
is more consistent with the CLI and makes it possible to add an
optional parameter or choices later without breaking compatibility.
Flatten everything to make it easier to map command-line flags to
json. The old structure was an illusion anyway because there was no
mechanism to enforce that things were in the right place. This also
helps with future flexibility.
The code was assuming everything was happening inside dictionaries.
Instead, make the dictionary key handler creatino explicit only when
iterating through dictionary keys.
Why? The main methods that create them return smart pointers so that
users can initialize them when needed, which you can't do with
references. Returning pointers instead of references makes for a more
uniform interface.
This is a massive rewrite of the help text and cli.rst section of the
manual. All command-line flags now have their own help and are
specifically index. qpdf --help is completely redone.
Handle optional choices in addition to required choices. Refactor the
way help options are added to completion to make it work with optional
help choices.
