Can open an assembly file and execute it on the GUI.
Loader instantiated when load method is called, so that if multiple programs are opened over time, a new loader is created each time. This avoids old data causing problems.
Added a line to reset the memory pointer each time a program is loaded to memory; this avoids bits of old programs being left behind and causing errors.
Adjusted opening files so that relevant directory is set as the default. Also, opening a file automatically clears memory contents of any old programs.
Added display().