Preliminary preparation for publishing to Sonatype
Add missing `x` and `y` fields to Oval glyph
Add Circle.radius field and configure Marker.size
Add examples/src/main/scala/glyphs/Prim.scala
Add GMapPlot and BoxSelectionOverlay
Add <<= (functional transformation) operator to Field
Add examples/src/main/scala/glyphs/Maps.scala
Override viewModel in BoxSelectionOverlay