oblicubes v0.1.2

Initial features

• oblicubesGrob() / grid.oblicubes() renders cubes using a 3D
  oblique projection. oblicubesGrob() returns a grid grob object while
  grid.oblicubes() also draws the grob to the graphic device. As
  a special case may also render a 2D primary view orthographic projection.
  Inspired by coolbutuseless's {isocubes} package.
• geom_oblicubes() provides a {ggplot2} geom wrapper to oblicubesGrob().
• oblicuboidsGrob() / grid.oblicuboids() renders cuboids using a 3D
  oblique projection. oblicuboidsGrob() returns a grid grob object while
  grid.oblicuboids() also draws the grob to the graphic device. As
  a special case may also render a 2D primary view orthographic projection.
  Inspired by cj-holmes's {isocuboids} package.
• geom_oblicuboids() provides a {ggplot2} geom wrapper to oblicuboidsGrob().
• xyz_heightmap() calculate x,y,z coordinates (and optionally colors) from a height matrix.
  An adaption of coords_heightmap() from coolbutuseless's {isocubes}.
• darken_face() is a function to darken the color of cube/cuboid faces.
  Meant to serve as the light argument of oblicubesGrob(), grid.oblicubes(), oblicuboidsGrob(), grid.oblicuboids().
• cheap_darken() is a function to darken colors by a certain "amount".
  Faster (but less "good") then colorspace::darken().
  A copy of an internal function from coolbutuseless's {isocubes}.