OpenSystemsDevelopment / qpdf

* Use unique_ptr in place of shared_ptr in some cases
* unique_ptr for arrays does not require a custom deleter
* use std::make_unique (c++14) where possible

None of these are in the public API.

Use get() and use_count() instead. Add #define
NO_POINTERHOLDER_DEPRECATION to remove deprecation markers for these
only.

This commit also removes all deprecated PointerHolder API calls from
qpdf's code except in PointerHolder's test suite, which must continue
to test the deprecated APIs.

PointerHolder will be replaced with shared_ptr, so let people start
moving.

add qpdf_oh_new_binary_unicode_string and qpdf_oh_get_binary_utf8_value

Let argv be a null-terminated array. There is already code that
assumes this, and it makes it easier to construct the arguments.

This makes it much more convention to use the initializeFromArgv
functions since you can use string literals.

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.

Use "file" consistently for specifying a file path. We use "filename"
when adding attachments for a completely different purpose.

Since the functionality of argument parsing has moved into QPDFJob,
these classes no longer need to be public. Their methods still have to
be in the library's binary interface so they can be tested in libtests.

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.

Use named functions rather than just end() for clarity.

All that's left now is input and output handling.

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