Fix the URL detection for relative paths

`$(elem).attr('href')` gets the value of `elem.getAttribute('href')`,
and `$(elem).prop('href')` gets from `elem.href`. they means slightly
different.

See also http://api.jquery.com/prop/
Fix some styles
Merge branch 'master' into fix
Move external libraries into `lib/`
Merge pull request #2 from Kroisse/fix

링크가 상대 경로일때도 처리하도록 고침