Better display of error messages. (#60)
Resolved #59: run_phantomjs() now checks that a port
is available before telling PhantomJS to start and listen on that port.
It also provides more informative error messages if unable to connect.
(#62)
Make sure stdout and stderr output is recorded.
Try to find locally-install phantomjs first.
Session$new() now checks that the phantomjs binary
was built with ghostdriver support.
First public release.