fix/shorten midi mapping functions for loop handling

Hey there! I find the MidiZoomSelect very handy. The handler function for the loop points crashed on me when reaching the end of the sample. The selection points were somehow more coarse than necessary, possibly because of the math.floor() you're doing. I fixed those things and shortened the code a bit, too. 

Some of your other tools look interesting too. Checking them out now. :-)