Add QFN-56 with 6.1mm EP
This is a format used by Intan RHD5000 series ICs.
ChipQuik IPC0031 breakouts also in this size.
The diagram doesn't specify tolerances, so use the same as the 5.9mm part.
Datasheet: http://intantech.com/files/Intan_RHD2000_series_datasheet.pdf
Previous MR: https://github.com/pointhi/kicad-footprint-generator/pull/267
Edited by John Beard