expose promise polyfill in a way that won't need code migration later

docs/api.md

@@ -18,4 +18,5 @@
 - [m.redraw](redraw.md)
 - [m.version](version.md)
 
-- [stream](stream.md)
+- [Promise](promise.md)
+- [Stream](stream.md)

docs/v1.x-migration.md

@@ -441,7 +441,7 @@ setTimeout(function() {
 }, 1000)
 ```
 
-The equivalent of `m.sync` is now `m.Promise.all`
+The equivalent of `m.sync` is now `Promise.all`
 
 ### `v0.2.x`
 
@@ -458,7 +458,7 @@ m.sync([
 ### `v1.x`
 
 ```javascript
-m.Promise.all([
+Promise.all([
     m.request({ method: 'GET', url: 'https://api.github.com/users/lhorie' }),
     m.request({ method: 'GET', url: 'https://api.github.com/users/isiahmeadows' }),
 ])