OpenSystemsDevelopment / qpdf

* Don't surprise people with deprecation warnings
* Provide detailed instructions and support for the transition

* 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

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.

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