Updates to example application cells

Ah I see. Best thing might be to keep them as you have them, and to just make sure that they're defined even in debug builds.

libmuslc's stdio routines will go a single serial port in all cells, so they should probably be used only for debug tracing (e.g. only via debug_printf()). 

We could perhaps make this clearer by renaming _puts(), _getchar() etc. to cell_puts(), cell_getchar(), to make it very clear that these are cell-specific functions.