As described in #2340, this provides a way to replace an old alias with a redirect. This makes it easier to migrate our URLs over time without making our matching patterns more complicated.
The 301 redirect is sent back to the requester. If a user pastes the aliased URL into the address bar, it'll be replaced in the browser with the new URL, which gently encourages them to migrate.
Close#2340
Close#2334
To avoid merge conflicts, I've deferred removing the aliasing logic in `prepareExamples`. That whole function will be refactored momentarily, and there's also #2339 open.
The term “url” is overloaded in services, to refer to the Shields route and also the API URL. Calling the Shields URL a “route” is on the whole more descriptive, and makes it clearer and more obvious which one of these we’re talking about. It’s a small thing, though seems like an improvement.
We have a few functions called `buildUrl`. I’ve renamed them to `buildRoute` when they refer to routes, and left them as `buildUrl` when they refer to API URLs.
I included a minor style tweak and some formatting cleanup in `TUTORIAL.md`.
1. Add validation to BaseSvgScrapingService and update readthedocs accordingly.
2. Rewrite vso and add more tests. Rename it internally to azure-devops. URLs are still `/vso` for now. Should we make a way to let a service register multiple URL patterns?
3. Handle shared code using a functional pattern instead of inheritance. This comes from a discussion https://github.com/badges/shields/pull/2031#issuecomment-417893819. I like the functional approach because it's more direct, nimble, and easy to reason about; plus it allows services to grow from a family of one to two more easily.
