Partially recast the router API to be a lot more intuitive. (#2469)

* Recast the router API to be a lot more intuitive.

Fixes #2387
Fixes #2072
Fixes quite a few issues reported on Gitter.

For `m.route.Link`:

- More intuitive
- More accessible
- More ergonomic
- It can be disabled
- It can be cancelled
- It can be changed
- Oh, and you can use it isomorphically.

For `m.route.prefix`

- You can *read* it.
- You can write to it, of course.
- It's literally just setting a property.

For the router itself (and the rest of Mithril):

- You can now `require("mithril")` and all its submodules without a DOM
  at all. There is a catch: you can't instantiate any routes, you can't
  mount anything, and you can't invoke `m.render` in any capacity. You
  can only use `m.route.Link`, `m.route.prefix`, hyperscript stuff, and
  `mithril/stream`, and you can use `m.request` with `background: true`
  if you use a global XHR polyfill. (You can't use `m.request` without
  `background: true` except with a DOM to redraw with.) The goal here is
  to try to get out of the way for simple testing and to defer the
  inevitable `TypeError`s for the relevant DOM methods to runtime.

  The factory requires no arguments, and in terms of globals, you can
  just figure out based on what errors are thrown what globals to
  define. Their values don't matter - they just need to be set to
  *something*, even if it's just `null` or `undefined`, before Mithril
  executes.

Had to make quite a few other changes throughout the docs and tests to
update them accordingly. Oh, and that massive router overhaul enabled me
to do all this.

Also, slip in a few drive-by fixes to the mocks so they're a little
easier to work with and can accept more URLs. This was required for a
few of the tests.

* Update changelog + numbers, add forgotten bundle option

* Add PR numbers to changelog [skip ci]

* Allow continuing to the next match by returning `false`.

* Update numbers again

docs/change-log.md

@@ -61,6 +61,18 @@
     - The `.schedule`, `.unschedule`, and `.render` properties of the former `redrawService` are all removed.
     - If you want to know how to work around it, look at the call to `mount` in Mithril's source for `m.route`. That should help you in finding ways around the removed feature. (It doesn't take that much more code.)
 - api: `m.version` has been removed. If you really need the version for whatever reason, just read the `version` field of `mithril/package.json` directly. ([#2466](https://github.com/MithrilJS/mithril.js/pull/2466) [@isiahmeadows](https://github.com/isiahmeadows))
+- route: `m.route.prefix(...)` is now `m.route.prefix = ...`. ([#2469](https://github.com/MithrilJS/mithril.js/pull/2469) [@isiahmeadows](https://github.com/isiahmeadows))
+    - This is a fully fledged property, so you can not only write to it, but you can also read from it.
+    - This aligns better with user intuition.
+- route: `m.route.link` function removed in favor of `m.route.Link` component. ([#2469](https://github.com/MithrilJS/mithril.js/pull/2469) [@isiahmeadows](https://github.com/isiahmeadows))
+    - An optional `options` object is accepted as an attribute. This was initially targeting the old `m.route.link` function and was transferred to this. ([#1930](https://github.com/MithrilJS/mithril.js/pull/1930))
+    - The new component handles many more edge cases around user interaction, including accessibility.
+    - Link navigation can be disabled and cancelled.
+    - Link targets can be trivially changed.
+- API: Full DOM no longer required to execute `require("mithril")`. You just need to set the necessary globals to *something*, even if `null` or `undefined`, so they can be properly used. ([#2469](https://github.com/MithrilJS/mithril.js/pull/2469) [@isiahmeadows](https://github.com/isiahmeadows))
+    - This enables isomorphic use of `m.route.Link` and `m.route.prefix`.
+    - This enables isomorphic use of `m.request`, provided the `background: true` option is set and that an `XMLHttpRequest` polyfill is included as necessary.
+    - Note that methods requiring DOM operations will still throw errors, such as `m.render(...)`, `m.redraw()`, and `m.route(...)`.
 
 
 #### News
@@ -68,7 +80,6 @@
 - Mithril now only officially supports IE11, Firefox ESR, and the last two versions of Chrome/FF/Edge/Safari. ([#2296](https://github.com/MithrilJS/mithril.js/pull/2296))
 - API: Introduction of `m.redraw.sync()` ([#1592](https://github.com/MithrilJS/mithril.js/pull/1592))
 - API: Event handlers may also be objects with `handleEvent` methods ([#1949](https://github.com/MithrilJS/mithril.js/pull/1949), [#2222](https://github.com/MithrilJS/mithril.js/pull/2222)).
-- API: `m.route.link` accepts an optional `options` object ([#1930](https://github.com/MithrilJS/mithril.js/pull/1930))
 - API: `m.request` better error message on JSON parse error - ([#2195](https://github.com/MithrilJS/mithril.js/pull/2195), [@codeclown](https://github.com/codeclown))
 - API: `m.request` supports `timeout` as attr - ([#1966](https://github.com/MithrilJS/mithril.js/pull/1966))
 - API: `m.request` supports `responseType` as attr - ([#2193](https://github.com/MithrilJS/mithril.js/pull/2193))
@@ -88,6 +99,7 @@
 - API: `m.buildPathname` and `m.parsePathname` added. ([#2361](https://github.com/MithrilJS/mithril.js/pull/2361))
 - route: Use `m.mount(root, null)` to unsubscribe and clean up after a `m.route(root, ...)` call. ([#2453](https://github.com/MithrilJS/mithril.js/pull/2453))
 - render: new `redraw` parameter exposed any time a child event handler is used ([#2458](https://github.com/MithrilJS/mithril.js/pull/2458) [@isiahmeadows](https://github.com/isiahmeadows))
+- route: `m.route.SKIP` can be returned from route resolvers to skip to the next route ([#2469](https://github.com/MithrilJS/mithril.js/pull/2469) [@isiahmeadows](https://github.com/isiahmeadows))
 
 #### Bug fixes