Added push and pop commands.

Signed-off-by: Charlotte Pierce <charlotte@malformed-bits.com>
Added sample plant.

Signed-off-by: Charlotte Pierce <charlotte@malformed-bits.com>
Turtle heading starts at 90 degreess (i.e., up).

Signed-off-by: Charlotte Pierce <charlotte@malformed-bits.com>
Added example commands for edge and node rewriting plants.

Signed-off-by: Charlotte Pierce <charlotte@malformed-bits.com>