Usage:
          - Semicolon at end of statement is optional.
          - Expression being any operation of:
            - binary operations: +, -, *, /, modulo: '%' or 'mod', pow: '^' or '**'
            - unary functions: abs, sin, cos, tan, asin, acos, atan, sqrt, ln, log, exp, ceil, floor
            - misc functions: step(edge, x), mix(x, y, a)
            - braces: (, )
          > draw 
          > draw sin(x)
          > clear
          > set_width x1, x2
          > set_height y1, y2
          > help
          > exit