Mod CONTRIBUTING to accept Github pull requests.
Unify version numbers for Clownfish and CFC.

Since both Clownfish and CFC will be released together in a single
Apache package, unify their version numbers.
Provide version numbers in all .pm files.
Add CFC CPAN prereqs, but avoid warning.

Reversing the logic (adding then conditionally deleting rather than
conditionally adding) means that the CPAN dist will generate a META.json
with the proper prereqs.
Adapt Lucy's update_version tool for Clownfish.
Udpate version to 0.4.0.
Use specific X.Y.Z version in Build.PL.

Otherwise, if we take it from CFC.pm the dist will be named
Clownfish-CFC-X.YYYZZZ.tar.gz when we want Clownfish-CFC-X.Y.Z.
Add CHANGES.
Remove extraneous material from LICENSE.

*   utf8proc
*   Snowball
*   US Constitution
Fix branding in INSTALL and README.

Use "Apache Clownfish" first, and use it as an adjective per trademark
guidelines.
Update release date in CHANGES.
Copy and adapt release_commands.pl from Lucy.