A to-do list for the Gviz package

General
   o check the plotting with small coordinates, do all track types align?

AnnotationTrack/GeneRegionTrack
   o speed up .prepareGene (may need a C code module)
   o deal with additional annotation features (UTRs, etc.)

DataTrack/AnnotationTrack => SNPsTrack?
   o issue: #5
   o new track type to handle LD information
   o ideally as heatmap with defined depth (range)
   o check following: snpStats (data structure), ldblock, gwascat
   o similar thing already implemented in LDheatmap

New docs with roxygen

Clean the code
   o styler::style_pkg(indent_by = 4, scope=I(c("spaces", "indention", "line_breaks", "tokens")))
   o formatR::tidy_dir("tests/testthat", comment=TRUE, blank=TRUE, brace.newline=FALSE, wrap=TRUE, args.newline=FALSE, width.cutoff=I(80), indent=4)
