Add SSL support for JRuby

- Implement MiniSSL for JRuby

- Modify `Binder` and `MiniSSL::Context` to to accommodate the fact
that Java SSL demands a java keystore rather than a key/cert pair

- Change the MiniSSL native extension interface to take a
`MiniSSL::Context` rather than a key/cert pair so that each extension
can grab keys off the context as appropriate
Merge pull request #530 from looker/jruby-ssl

SSL support for JRuby