Improved EXAM mode and inital WIP of Block Exam

If is pressed enter or a command is called without writing an address,
LADDRESS is preserved instead of being overwrite by 0.

Initial work on block examine mode
Print address code move to a subrutine
Block examine mode working

It could be improved to display ASCII representation of RAM on the right
marging of the screen. This could be a future TODO
Updated README.md with info about the code monitor