[LIBMIDI]in libmidi Track object Event and EventPulses should be put together

[allan-simon]

in a std::pair or something otherwise in a lot of place in the code , we're obliged to do an old school

for (i = 0 etc.

with Events to then get the associated EventPulses, using a Pair will permit to use the mode readable and less error prone for ( value : collection) notation