support user-forced line-breaks in custom block labels

Creating a custom block label-fragment named “$br” forces a new line in
all block instances. You can also select “line break” from the
label-fragment’s context menu, same as selecting a symbol.
This is really ugly, I know, I know.
But I need it to play with the micro:bit and the calliope boards.

byob.js

@@ -107,7 +107,7 @@ SymbolMorph, isNil, CursorMorph, VariableFrame, WatcherMorph, Variable*/
 
 // Global stuff ////////////////////////////////////////////////////////
 
-modules.byob = '2017-January-03';
+modules.byob = '2017-January-20';
 
 // Declarations
 
@@ -236,6 +236,8 @@ CustomBlockDefinition.prototype.blockSpec = function () {
     parts.forEach(function (part) {
         if (part[0] === '%' && part.length > 1) {
             spec = myself.typeOf(part.slice(1));
+        } else if (part === '$br') {
+            spec = '%br';
         } else {
             spec = part;
         }
@@ -2463,6 +2465,8 @@ BlockLabelFragmentMorph.prototype.userMenu = function () {
             name
         );
     });
+    menu.addLine();
+    menu.addItem('\u03A0 ' + localize('line break'), 'br');
     return menu;
 };
 
@@ -2922,6 +2926,7 @@ InputSlotDialogMorph.prototype.symbolMenu = function () {
             '$' + symbol
         ]);
     });
+    symbols.push(['\u03A0 ' + localize('line break'), 'br']);
     return symbols;
 };
 

history.txt

@@ -3319,3 +3319,4 @@ Fixes:
 ------
 * Blocks: improved inspectability of local variables
 * GUI: improved library browser, thanks, Michael!
+* BYOB: support user-forced line-breaks in custom block labels