Please remove cl-rainbow (will be superseded by cl-ansi-text)

[taksatou]

Although I just requested registration of cl-rainbow few weeks ago, pnathan, who is the author of cl-ansi-text, and I discussed our projects, and decided to merge cl-rainbow into cl-ansi-text.

I apologize for bothering you, but can you please remove cl-rainbow?

refs:

• https://github.com/pnathan/cl-ansi-text
• code duplication taksatou/cl-rainbow#1
• Please add cl-rainbow #449