* Prefer `PROJECT_{SOURCE,BINARY}_DIR` to `CMAKE_` ones
* Extend use of 3rd-party dir vars to reduce duplication
* Fix typo in submodule repo name
* Remove `CURL::libcurl` target fallback
The target is always available since CMake 3.12, which is our current
minimum version.
* refactor: include <memory> when using shared_ptr or unique_ptr
* refactor: include <cstdio> iff we use it
* refactor: include <cstring> iff we use it
* refactor: include <cstdlib> iff we use it
* refactor: include <string_view> or <string> iff we use it
* refactor: include <array> iff we use it
* refactor: include <ctime> iff we use it
* refactor: include <cctype> iff we use it
* refactor: misc #include cleanups in libtransmission
Mike Gelfand