Spanish 'adder' page translation

See #17
Spanish 'code' page translation

See #17
Spanish 'instruction pointer' page translation

See #17
Spanish 'cpu' page translation

Fixes #17
I decided not to translate the cpu.js file so it's not _that_ difficult to maintain.
There are a few words which could have been translated ('address', 'value'), but I
think it's not worth it.