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]

querystring/tests/test-parseQueryString.js

@@ -97,16 +97,4 @@ o.spec("parseQueryString", function() {
 		var data = parseQueryString("a=1&b=2&a=3")
 		o(data).deepEquals({a: "3", b: "2"})
 	})
-	o("continues to append to arrays between calls", function() {
-		var data = {}
-		parseQueryString("a[]=1&a[]=2", data)
-		parseQueryString("a[]=3&a[]=4", data)
-		o(data).deepEquals({a: ["1", "2", "3", "4"]})
-	})
-	o("continues to append to objects between calls", function() {
-		var data = {}
-		parseQueryString("a[b]=1&a[c]=2", data)
-		parseQueryString("a[d]=3&a[e]=4", data)
-		o(data).deepEquals({a: {b: "1", c: "2", d: "3", e: "4"}})
-	})
 })