regen_charmonizer.pl script for Clownfish

regen_charmonizer.pl now accepts a command-line argument which contains
the path to the Charmonizer tree. If this argument is missing, default
to '../charmonizer' from the Clownfish root.
Regenerate charmonizer.c
Installation instructions
Add CONTRIBUTING file

Copied from Lucy with minor adjustments.
Add LICENSE file
Add NOTICE file
Add README file
Copy lemon directory from Lucy
Fix path to lemon directory
Add global .gitignore file