Additional features required

[rcalcagno]

As in the 10/30 meeting, two additional features have been added to the requirement list:

1. A DUMP of the Pico's internal status following an error, so to be able to trace significant status data
2. A "previous operation status" short string, which will hold the relevant info. It could be either SUCCESFUL, or if an error occured, an error code or short string with the cause. This should be retrievable from BASIC with an appropiate command