https://bioconductor.org/packages/devel/bioc/vignettes/IRanges/inst/doc/IRangesOverview.pdf
- findOverlaps => detect overlaps
- coverage => count number of ranges over each position
- nearest => find nearest neighbor ranges (overlapping is zero distance)
- preced / follow</em> => find non-overlapping nearest neighbors on specific direction
- disjoin => make the ranges non-overlapping
- set operations are implemented in 2 ways (1 normal, 1 applied to each pair)