Call CC0 copying information instead of license

Before this PR, this repo said that its "license" was CC0. CC0 is a
public domain dedication, not a license. (See
<https://creativecommons.org/faq/#how-do-cc-licenses-operate>). This
change makes this repo refer to CC0 as copying information.

The term "copying" was chosen to make this repo more closely follow CC's
recommendation for applying CC0 to computer software:
<https://wiki.creativecommons.org/wiki/CC0_FAQ#May_I_apply_CC0_to_computer_software.3F_If_so.2C_is_there_a_recommended_implementation.3F>

Fixes #45.

Author: Jayman2000

LICENSE renamed to COPYING

@@ -264,10 +264,10 @@ Consortium.
 - [Locale (computer software) - Wikipedia][wikipedia-locale]
 
 
-## License
+## Copying
 
 [![CC0 1.0 Universal (CC0 1.0) Public Domain Dedication button][cc-zero-png]][cc-zero]
-[`LICENSE`](LICENSE): The text of the Creative Commons public licenses is
+[`COPYING`](COPYING): The text of the Creative Commons public licenses is
 dedicated to the public domain under the [CC0 1.0 Universal (CC0 1.0) Public
 Domain Dedication][cc-zero].