simple LUT parser

# [CRATES.IO](https://crates.io/crates/lut_parser)

Cube format based on spec at https://wwwimages2.adobe.com/content/dam/acom/en/products/speedgrade/cc/pdfs/cube-lut-specification-1.0.pdf

Pretty much a Rust port of this JS example: https://github.com/thibauts/parse-cube-lut/blob/master/index.js