def insertion(self, loc, seq, tsdlen=0):
        tsd = self.seq[loc:loc+tsdlen]
        self.seq = self.seq[:loc] + tsd + seq + self.seq[loc:]
inserts seq after position loc, adds taret site duplication (tsd) if tsdlen > 0
dataset/ETHPy150Open adamewing/bamsurgeon/bamsurgeon/mutableseq.py/MutableSeq.insertion