1.5.2

• AppContext struct renamed to GEMContext (with backwards compatibility with previous name);
• New methods ::setDrawMenuCallback() and ::removeDrawMenuCallback() for managing optional callback that is invoked at the end of ::drawMenu() call;
• Method ::getCurrentAppearance() made public;
• private access specifiers changed to protected to make it possible to access internal fields and methods from within user-defined derived (inherited) classes, allowing to extend functionality of GEM;
• Optional "Advanced Mode" introduced, disabled by default but can be enabled via config.h or GEM_ENABLE_ADVANCED_MODE flag; when enabled some of the internal methods are made virtual to make it possible to override those methods in own sketch, allowing further customization and modification of GEM; more features of Advanced Mode may be added in the future;
• Readme updated accordingly.