OpenSystemsDevelopment / qpdf

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.

This is all that ever worked. The test suite was trying to do
something different from ClosedFileInputSource.

When possible, use `for (auto&` or `for (auto const&` when iterating
using C++-11 style iterators.