Dedup stats

[sergpolly]

@golobor finally, I've made something to address https://github.com/mirnylab/pairsamtools/issues/55

Sorry it took so long!

This more of a conversation starter, rather than the final version.
It is working correctly on your test mock.4dedup.pairsam, producing correct stats and outputs (checked for different mismatch radii).

Haven't tested performance or larger data.
Once we finalize this thing it would be much easier to update distiller

[golobor]

apologies for the delay! This looks very good, thank you!
What else should be done in your opinion?

[sergpolly]

Thank you! Now we should obviously fix the distiller open2c/distiller-nf#80

I'd also consider the optical dedups thing https://github.com/mirnylab/pairsamtools/issues/59
this addition, should be easy now: https://github.com/mirnylab/pairsamtools/issues/54
and maybe this, if I knew what is it: https://github.com/mirnylab/pairsamtools/issues/56

Maybe stats could be Cythonized a little bit - but I have to measure the performance at first