Clarify pathname docs, follow spec with fragments (#2448)

* Clarify pathname docs, follow spec with fragments

- Valid URLs must not contain a `#` within its fragment.
  https://github.com/MithrilJS/mithril.js/issues/2445
- Our docs were a little confusing and misleading - `m.pathname` isn't
  aware of URLs, just path names.
- Removed the relevant extension to `m.parseQueryString` required to
  support the hash parsing extension. Now we just shave it off and
  ignore it.
- Fix support for arbitrary prefixes, so prefixes like `?#` are
  handled correctly.
- Add a bunch of tests to cover various areas of confusion and unusual
  edge cases.

* Update with PR [skip ci]

test-utils/xhrMock.js

@@ -36,6 +36,7 @@ module.exports = function() {
 			}
 			this.open = function(method, url, async, user, password) {
 				var urlData = parseURL(url, {protocol: "http:", hostname: "localhost", port: "", pathname: "/"})
+				args.rawUrl = url
 				args.method = method
 				args.pathname = urlData.pathname
 				args.search = urlData.search
@@ -56,7 +57,7 @@ module.exports = function() {
 				var self = this
 				if(!aborted) {
 					var handler = routes[args.method + " " + args.pathname] || serverErrorHandler.bind(null, args.pathname)
-					var data = handler({url: args.pathname, query: args.search || {}, body: body || null})
+					var data = handler({rawUrl: args.rawUrl, url: args.pathname, query: args.search || {}, body: body || null})
 					self.status = data.status
 					// Match spec
 					if (self.responseType === "json") {