Version 1.8.0

• It is now possible to read, write and manipulate additional image metadata
  fields stored in JSON "sidecar" files like those used by the Brain Imaging
  Data Structure. readNifti and writeNifti each gain a "json" argument,
  and the new imageAttributes function can be used to get and set attributes
  for images. Conversion to or from JSON requires the jsonlite package;
  this is an R-only feature for now.
• If a plain string is passed to lyr as the "scale" argument and doesn't
  match a known scale name from the shades package, it is now assumed to be
  a single literal colour name. (Prompted by Ellyn Butler, issue #36.)
• Initialisation of the complex NA value in C++ code has been simplified to
  avoid remaining compilation problems on some platforms. (Issues #35 and #38.)