Baseline support

Summary:
Added baseline support (see #132)

You have the ability for a custom baseline function (```float(*YGBaselineFunc)(YGNodeRef node);```) to return whatever baseline you want.
Closes https://github.com/facebook/yoga/pull/317

Reviewed By: splhack

Differential Revision: D4385061

Pulled By: emilsjolander

fbshipit-source-id: cb8a59a09237c840fa3e21753ab68239997dab0c

java/com/facebook/yoga/YogaAlign.java

@@ -17,7 +17,8 @@ public enum YogaAlign {
   FLEX_START(1),
   CENTER(2),
   FLEX_END(3),
-  STRETCH(4);
+  STRETCH(4),
+  BASELINE(5);
 
   private int mIntValue;
 
@@ -36,6 +37,7 @@ public enum YogaAlign {
       case 2: return CENTER;
       case 3: return FLEX_END;
       case 4: return STRETCH;
+      case 5: return BASELINE;
       default: throw new IllegalArgumentException("Unkown enum value: " + value);
     }
   }