Release candidate version of MixMHC2pred-2.0

Pre-release version of the major update of MixMHC2pred-2.0.

• This new version allows for pan-allele predictions for human and non-human MHC-II alleles.
• The implementation vastly changed; it is now based on multiple neural networks and it was trained on a much larger MHC-II peptidomics dataset.
• Please note that the format of the input and output files have changed, as well as the available input arguments (see README for details of the input/output files and usage).