Treat registerRoute('/foo/:bar', ...) as exact match in v3

[jeffposnick]

Library Affected:
workbox-routing

Following up from #1011, in v3 we are going to stop creating ExpressRoutes implicitly whenever there's a string argument passed to the registerRoute() helper.

Instead, strings will be tested for an exact match, either against the url.path (if the string begins with '/') or against the url.href (if the string begins with http).

We'll continue the logging that #1011 introduces, and ensure that we direct developers to documentation about constructing an equivalent RegExpRoute and/or creating their own custom matchHandler as alternatives.

[gauntface]

SGTM.

Worth calling out that matches for strings not starting with http should only match same-origin requests - same as regular expressions.

I'm still open to supporting an express style "matcher" if developers want it but I'm fairly sure a RegExp will be easy to replace the express routes in most cases.