Update hex logo

[trevorld]

• Currently a square logo of a ggplot2 plot with a patterned hex in it.
• Could instead be a hex logo as is "traditional" for R packages.
• Maybe use affiner::grid.isocube() to make a "isometric cube" style "hex" logo? https://trevorldavis.com/R/affiner/dev/reference/isocubeGrob.html