Added Export Symbols command

Export Symbols.sketchplugin

@@ -0,0 +1,31 @@
+var layers = [[doc currentPage] layers],
+    document_path = [[doc fileURL] path].split([doc displayName])[0],
+    currentFilePath = [[doc fileURL] path];
+
+// Loop through layers, picking symbols:
+var allSymbols = {}
+for (var i=0; i < [layers count]; i++) {
+  var current = [layers objectAtIndex:i],
+      currentID = current.sharedObjectID()
+
+  if (currentID != null ) {
+    // 'current' is a symbol instance
+    // make sure we're not storing duplicated instances:
+    allSymbols[currentID] = current
+  }
+}
+
+if(Object.keys(allSymbols).length == 0){
+  [doc showMessage:"Please place a symbol on the canvas"]
+} else {
+  for (var currentID in allSymbols) {
+    var currentSymbol = allSymbols[currentID],
+        symbolName = [currentSymbol name],
+        exportFilename = document_path + "/" + symbolName + ".png",
+        slice = [[MSSliceMaker slicesFromExportableLayer:currentSymbol] firstObject]
+
+    slice.page = [[doc currentPage] copyLightweight]
+    slice.format = "png"
+    [[MSSliceExporter dataForRequest:slice] writeToFile:exportFilename atomically:true]
+  }
+}