conditional os in UI xml, add system dialog file open on osx, check api format or error message when opening a document, per-char text wrap on NodeText, additional info on create doc dialog like working path

src/node_text.h

@@ -17,6 +17,7 @@ public:
     virtual void restore_context() override;
     virtual void parse_attributes(kAttribute ka, const tinyxml2::XMLAttribute* attr) override;
     void set_text(const char* s);
+    void set_text_format(const char* fmt, ...);
     void set_font(kFont fontID);
     virtual void draw() override;
 };