Add a workspace for standalone development.

Rebel.xcworkspace/contents.xcworkspacedata

@@ -0,0 +1,13 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<Workspace
+   version = "1.0">
+   <FileRef
+      location = "group:Rebel.xcodeproj">
+   </FileRef>
+   <FileRef
+      location = "group:External/expecta/Expecta.xcodeproj">
+   </FileRef>
+   <FileRef
+      location = "group:External/specta/Specta.xcodeproj">
+   </FileRef>
+</Workspace>