MISO: fixed the 'marginal' sampler, if some reads do not match any isoforms.
MISO: fixed a bug when not the 'reassign' sampler was used.
MISO: fixed a bug in the 'classes' sampler when some reads do not match any isoforms.
Fixed a bug in the calculation of the number of reads in the various classes when some reads do not match any isoforms.
Updated R interface of some internal functions, to allow testing.