Recipe for pier-mode

Summary: Emacs Major mode for Pier-formatted text files.

Association with the package: I am the maintainer.

Repository: https://github.com/DamienCassou/pier-cl

Communication with package maintainer: none, the package was already
ready.

Tests: the package builds and installs properly.
Merge pull request #1123 from DamienCassou/recipe-pier-mode

Recipe for pier-mode