Scripts to help with executable debhelper files

 Debhelper (in compat level 9 and above) allows its config files to be
 executable, and uses the output of suchs scripts as if it was the
 content of the config file.
 .
 To ease and standardize the most common tasks, this package provides
 a few solutions to help constructing such executable scripts:
 .
  * A way to ease variable substitution, from environment variables or
    dpkg-architecture.
  * An extension to dh_install, with the ability to rename files.