LICENSE: Use the WTFPL

The DO WHAT YOU WANT PUBLIC LICENSE might not already be in
distributions' whitelists.

And rename to COPYING as that's what autotools expect.
Use C instead of shell scripts

This is quicker, as it doesn't need to copy the whole file to a
temporary directory. It also doesn't need to copy it to a known
world-writable location causing security issues.
Merge pull request #1 from hadess/master

Port to C