Rewrite styled-jsx/css (#422)

Split the old `css` tag in:

* `css`: generates scoped styles
* `css.global`: generates global styles
* `css.resolve`: resolves styles to an object which contains the scoped `className` and a drop-in `styles` element to render the styles

Also introduces a macro (see babel-plugin-macros) for `css.resolve`

css.js

@@ -1,5 +1,19 @@
-module.exports = function() {
+function notTranspiledError(name) {
   throw new Error(
-    'styled-jsx/css: if you are getting this error it means that your `css` tagged template literals were not transpiled.'
+    'styled-jsx/css: if you are getting this error it means that your `' +
+      name +
+      '` tagged template literals were not transpiled.'
   )
 }
+function css() {
+  notTranspiledError('css')
+}
+css.global = function() {
+  notTranspiledError('global')
+}
+css.resolve = function() {
+  notTranspiledError('resolve')
+}
+module.exports = css
+module.exports.global = css.global
+module.exports.resolve = css.resolve

macro.js

@@ -0,0 +1 @@
+module.exports = require('./dist/macro')