Median

Hi,

This includes the median diff that intends to fix #18. I am not sure if a pull request is better than simply applying the diff since the commit history might be confusing (I didn't create issues for bugs, accidentally removed then added example meta-files, and etc.). But this decision can be postponed to the phase of merging median into master.

I added support for 1st and 3rd quartiles, but this is really an initial commit, and mostly for debugging.

I think our roadmap should be:
1- Testing this on a couple of large datasets, by counting points below the nth quartile values and checking if it is actually close enough to expected frequency.
2- If it fails averaging, trying to estimate optimum b and k values, because we saw that modifying those fixed erroneous estimates before.