OpenSystemsDevelopment / qpdf

If some keys depend on others, we have to check up front since there
is no control of what order key handlers will be called. Anyway, keys
are unordered in json, so we don't want to depend on ordering.

This was used, but it no longer is, so let's not keep the extra
complexity around.

Replace most of the calls to QUtil::copy_string with this instead.

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.

* Make it a runtime error, not a logic error
* Include additional information
* Capture it properly in checkLinearization

Create a computationally and memory efficient implementation of name
and number trees that does binary searches as intended by the data
structure rather than loading into a map, which can use a great deal
of memory and can be very slow.

Turns out unreadCh is much more efficient than seek(-1, SEEK_CUR).
Update comments and code to reflect this.

We need to run qpdf --show-crypto.