LED matrix display - MD_Parola, MD_MAX72xx and MD_MAXPanel

I have reworked the MD_MAX72xx libraries for Parola and the whole system can now run on the more generic hardware modules with connectors at the top and bottom. Library version 2.2 is available in the repository (link below). You need to use the compiler switch USE_PAROLA_HW to switch the code in the library between hardware types. Please read the accompanying html documentation.

Thanks to Mel for Beta testing!