Provide a way to set a timeout

[timmc-edx]

Since this makes a network call, it would be good to have a way to cap the total time that this call can take, e.g. if the API is down or unreachable at the moment.

Most users of this library are likely using it on a login or registration request in an advisory fashion and would rather fail the lookup quickly rather than wait 30 seconds for a response.

Perhaps it could be threaded through the options, at least for the check call?

[dlo]

fixed in #6