Obtaining counts of CpG quartets

[stephenshank]

First, thank you for your work on this package, it is very impressive and useful!

I am curious as to whether the CpG quartet counts can be obtained as a byproduct of the epipolymorphism calculation. After reading the documentation it seems like this is a feature request. I ask because we are interested in calculating temporal changes in epiallele frequencies for polymorphic loci in AML.

I would envision another 16 columns in the output table, corresponding to each possible quartet.