Implemented full adder

- I guessed early on it would only take two half adders, due to adding
any more then two would only create the same output
- I found that the result sum and carry could not come from a half
adder because it had to be 1 and 1, which never happens.
- From this I guessed that the final carry had to be manipulated in
some way.
- I guessed to OR the first carry with the second to get the result.