Silly Logo turtle

---------------+
               |      , ,
               +------())*
                      ' '

Really darn simple Logo-like program.

Available commands are:

• f - forward 1 step
• b - backward 1 step
• r - right 90 degrees
• l - left 90 degrees
• @ - repeat last non-@ commands n times or repeat *every* previous command if called without argument

After each command you can specify a number, eg:

• f4 - 4 steps forward
• l2 - 180 degrees
• @3 - repeat last 3 commands

You must separate each instruction with a semicolon `;`

Example program to draw a rectangle would look like this:

f4;r;@;@;@;

and a program to draw a letter P would look like this:

f8;r;f4;@2;@2;