fixed version for 0.9 tag
Remove excessive filter calls on is_valid_user. The original issue is fixed in YOURLS core r795.
update version to 1.0
Create README.md from googlecode project

Copied the readme from https://code.google.com/p/yourls-authmgr-plugin/
Added LICENSE with GPLv3 license

as indicated by https://code.google.com/p/yourls-authmgr-plugin/