Changed 'public' and 'private' keywords to 'publicKey' and 'privateKey'.

Changed 'public' and 'private' keywords to 'publicKey' and 'privateKey'
because these are FutureReservedWords in strict mode of ECMAScript and
can be a problem when using Google Closure.

See http://www.ecma-international.org/ecma-262/5.1/#sec-7.6.1.2
Merge pull request #2 from s-k/master

'public' and 'private' keywords are a problem if using Google Closure