Export the Emacs command to recipe environments
Do not override $EMACS env var
Evaluate VERSION just once
Automatically install packages before build
Add clean-all target
Merge branch 'simplify-makefile'

* simplify-makefile:
  Add clean-all target
  Automatically install packages before build
  Evaluate VERSION just once
  Do not override $EMACS env var
  Export the Emacs command to recipe environments