nodemcu-firmware: Adding an error traceback to panic()

As part of my LCD patch, I also reimplemented the Lua error traceback, so that by default an error give a proper Lua stack traceback, rather the a one-line goodbye. However, the RTS still has a catch-all panic() to trap any unprotected error calls. This puts out a very unhelpful error message: PANIC: unprotected error in call to Lua API (<Lua routine name>). It just struck me that it would be better to provide a proper Lua traceback. Is this a good idea?

This is a fairly easy change.