Fix leveldb.org link in README.md

Was using relative url, which results in links like https://github.com/Level/leveldb.org/blob/master/leveldb.org, instead of http://leveldb.org.
Merge pull request #17 from pskupinski/fix-readme-leveldb-site-link

Fix leveldb.org link in README.md
fix invalid link in footer
Merge pull request #18 from Level/fix-link

fix invalid link in footer
gh-pages update