Fix up readme

This changes markdown style to be more consistent with the usual
markdown style. Also, importantly, this changes the plugin license
requirements to require an OSI-approved license instead of WTFPL.
WTFPL is basically public domain, and doesn't work in a number of
countries. You can't really use it for serious projects.
Update licensing requirements per IRC discussion
Including reformatted and updated readme.md. Closes #64
Fixed bad merge on README.md.
Update README
Fix minor formatting issue
Removed entity interaction restrictions from planet protect, as it prevents opening doors and has little griefing potential.