Optiona labels with type annotations.

Added examples.
See #585

Author: cristianoc

tests/printer/expr/expected/record.res.txt

@@ -74,7 +74,7 @@ let r = {
 }
 let r = {a /* a */, b /* b */}
 
-let r = {x: @optional None, y: @optional None, z: @optional None}
+let r = {x: @optional None, y: @optional None, z: (@optional None: tt)}
 
 let z = name => {@optional name, x: 3}
 
@@ -83,7 +83,7 @@ let z = name => {@optional name, x: 3}
 let z = name => {name, @optional x}
 
 let _ = switch z {
-| {x: @optional None, y: @optional None, z: @optional None} => 11
+| {x: @optional None, y: @optional None, z: (None: tt)} => 11
 | {@optional name, x: 3} => 42
 | {name: @optional dd, x: 3} => 42
 }

tests/printer/expr/record.res

@@ -64,7 +64,7 @@ let r = {
 }
 let r = {a /* a */, b /* b */}
 
-let r = {x: @optional None, y: @optional None, z: @optional None}
+let r = {x: @optional None, y: @optional None, z: @optional (None:tt)}
 
 let z = name => { name : @optional name, x: 3}
 
@@ -73,7 +73,7 @@ let z = name => { @optional name, x: 3}
 let z = name => { name, @optional x }
 
 let _ = switch z {
-  | {x: @optional None, y: @optional None, z: @optional None} => 11
+  | {x: @optional None, y: @optional None, z: @optional (None:tt)} => 11
   | {name:  @optional name, x: 3} => 42
   | {name:  @optional dd, x: 3} => 42
 }