Discover PLD NR version using 'git describe'
commented out packages not available in th-2012
Boot image layout and content fixes

– use template with @variables@ for boot image
– add README file
– move PLD NR files to /pld-nr-@bits@/ so two archs can be stored in a
  single directory
A bit more user friendly CalledProcessError messages
Optional memtest86 and memtest86+ added
Verify requirements before building
Documentation updates

– AUTHORS file added
– LICENSE file added
– README.md updated