Merge pull request #14 from scorphus/master

Support recently released tornado 3.2.1
Allow specifying the protocol to be used

Most often one will use HTTP, on any port. Yet, it may be necessary
to use HTTPS, such as in authenticated/authorized accesses.

Both positioning the new `protocol` argument in the end and using
`'http'` as it's default value guarantee backward compatibility.

Also, support all upcoming releases of tornado 3.2.* branch.