games/asciiquarium: Clean up, install docs & set license

• Standardize COMMENT
• Set LICENSE
• Fix shebang lines
• Install documentation
• Define do-test
• Extend the pkg-descr a little bit

Reviewed by: krion
Approved by: krion (mentor), maintainer (timeout, > 14 days)
Differential Revision: https://reviews.freebsd.org/D19533