Update class syllable + evaluation with ngram on phone

Added a class ngram for syllable (separated as now but could be merged
with orginal class, depend on what we want to do ut of it) => by the
way if I did not do any mistake, the bigram on syllables (which is
pretty close to our permutation model I guess) underestimates the nb of
neighbors…
Added also a function of evaluation for the ngram but is not fully
ready yet as the cpd of ngram need to be changed to smoothed (which is
already implemented in the class, but is had to change it manually as
for now - line 90)
the evaluation module can be called using --fnc "evaluate", you can
also change the size of the training set: --train 0.5 means that 50% of
the total corpus (selected at random) will be use for training.