graphics/R-cran-bmp: New port

bmp provides the ability to read Windows BMP format images in R.
Currently limited to 8 bit greyscale images and 24,32 bit (A)RGB
images. Pure R implementation without external dependencies.

Approved by: fuz (mentor), jrm (mentor)
Reviewed by: fuz (mentor), jrm (mentor), mat (previous revision)
Differential Revision: https://reviews.freebsd.org/D22680