Indexlr mx filter

[aafshinfard]

For filtering some unwanted minimizer kmers, we used to mask them (disqualifying them from generating minimizes by setting their hash value to max) which allowed some other adjacent kmers to develop false minimizers. This code enables an alternative approach: allow the unwanted kmers to generate minimizers, but then don't output minimizers originated from unwanted kmers.

This code does not change the default functionality of indexlr and supposedly does not run slower as it involves only a couple of additional if statements. I am planning some extensive testing and if they showed the alternative approach results in better results we will discuss changing the default behavior of indexlr.