longer intro, alpha preview
document database
Fix some wiki links in the README.
Merge pull request #50 from ewanmellor/fix-wiki-links

Fix some wiki links in the README.
Make Persona authorizer more tolerant of variant forms of origin URL

I.e. different capitalizations of "http", adding explicit port 80, etc.
Fixes #49
Doc-comment tweaks.
Made -[CBLModel markNeedsSave] public.