Add resistor-color exercise

[BNAndras]

Related to #675

[cmcaine]

Thanks for the PR.

Please apply changes from review, otherwise same as others: approaches file would be nice, but not necessary.

[cmcaine]

I applied the changes. Please either:

• merge
• or add approaches and re-request review
• or dispute changes

[BNAndras]

I don't have write access to the repo so I can't merge. However, since you wanted approaches written, I can take a look at that. I'm not sure how interesting that would be. I think it'd just be use a collection or use the if-else constructs. I can work on that next week though.