Fix constness of some PortDescriptor members.
Fix conflict in the makefile.
Allow to enumerate all MIDI ports from all APIs.
Add configure options to enable runtime pointer and thread checks.

Modern versions of gcc and clang can compile files in a way that they
can detect bad access to memory as use after free or array overflow
when it happens, which improves the debugging of such errors.
Partly fix an issue of the JACK backend that loses data and may cause segmentation faults.
Close the JACK independently from sending data.

The client may be unable to get a write buffer for some reason.
Check whether the JACK write buffer exists before sending MIDI data.
Store API parameters for later usage and allow to choose the order of API detection.

Both changes are needed to provide virtual ports from the all API seclection.
Implement virtual ports for rtmidi::ALL_API
Update input tests/examples for rtmidi::ALL_API.
Update the documentation to reflect the last changes to RtMidi