farver 2.0.0

• Added a NEWS.md file to track changes to the package.
• Remove Rcpp dependency for faster compilation. (#6)
• Add support for Lch(uv) (Hcl) for parallel to grDevices::hcl() (#9)
• Add encode_colour() for converting colours in any colourspace into #RRGGBB
  format (#7)
• Add decode_colour() for converting hexstrings into any colourspace
• Fix bug in luv conversion where 0 in the l channel resulted in NaN results
  (#12)
• Provide a family of channel manipulation functions to directly manipulate
  encodes strings