execute a program with a string assignment statement
execute a program with IF statements
map characters to character sprite coordinates
print a character at a designated location on the 'screen'
print a line of characters on the 'screen'
print multiple lines on the 'screen'
rename and reorder some classes
refactor BoolExpBuilder to use existing helpers
add keys.* files -  begin integrating the classes into a working app
echo character for pressed keys on the 'screen'