Extract input_tape method
Remove rules that put machine into an accept state

Because it is enough that this machine becomes 'stuck'
Simplify addition by merging states 4 and 5
Use 'X' for deletions and delete most significant bit first

To reduce number of rules required and remove the need for state 2
Use 'X' rather than blank to separate input from output

To reduce the number of rules and remove state 3
Normalize states

By changing 4 to 2 and 6 to 3
Extract initial_state method
Give states names
Remove unused rule
Merge pull request #1 from mocoso/tom_challenge

Reduce numbers of states and rules for Tom's book club challenge