Add mask to atom selection

Prevent the matching pursuit algorithm to select close atoms in time &
frequency
Use numpy.count_zero in mp iteration
Add update mdct fonctionnality

Allow to update the atoms that have been changed instead of proceed a
new mdct algorithm
Add atom method

Return a single atom defined by the size of the signal and its atom index
Use mdct update for the mask instead of full mdct
Merge branch 'matching-pursuit'

Conflicts:
	mp.py