Always expose stream on m.stream, use unpkg for docs (#1535)

... and document how streams are exposed in when loaded as <script> in global context

docs/stream.md

@@ -40,6 +40,14 @@ Streams are NOT bundled with Mithril's core distribution. To include the Streams
 var Stream = require("mithril/stream")
 ```
 
+You can also download the module directly if your environment does not support a bundling toolchain:
+
+```markup
+<script src="https://unpkg.com/mithril-stream"></script>
+```
+
+When loaded directly with a `<script>` tag (rather that required), the stream library will be exposed as `window.m.stream`. If `window.m` is already defined (e.g. because you also use the main Mithril script), it will attach itself to the existing object. Otherwise it creates a new `window.m`. If you want to use streams in conjunction with Mithril as raw script tags, you should include Mithril in your page before `mithril-stream`, because `mithril` will otherwise overwrite the `window.m` object defined by `mithril-stream`. This is not a concern when the libraries are consumed as CommonJS modules (using `require(...)`).
+
 ---
 
 ### Signature

stream/stream.js

@@ -113,4 +113,5 @@ createStream.combine = combine
 createStream.HALT = HALT
 
 if (typeof module !== "undefined") module["exports"] = createStream
-else window.stream = createStream
+else if (typeof window.m === "function" && !("stream" in window.m)) window.m.stream = createStream
+else window.m = {stream : createStream}