Redo build process for browsers and node. Update examples.

We now rely on browserify for building browser-specific versions of the JS
SDK. This can be initiated by running 'npm run build-js'. Node versions are
unaffected.

browser-index.js

@@ -0,0 +1,4 @@
+var matrixcs = require("./lib/matrix");
+matrixcs.request(require("browser-request"));
+module.exports = matrixcs; // keep export for browserify package deps
+global.matrixcs = matrixcs;