Make example project consume pod via Podfile again.

I know this looks like a big PR, but all I did is remove the duplicate ```Luhn.h``` and ```Luhn.m``` in the example project and move its contents to the other copies in ```Algorithm Class``` which is where the ```podspec``` is looking for the files. (So the new stuff you wrote today is in now in the ```Algorithm Class``` directory.)

You don't need to worry about keeping the old copies of the ```Luhn``` classes because Cocoapods uses git tags to keep track of which version to use.

When you pull this, make sure to run ```pod install``` from the ```Example Project``` directory. I've made sure the example app and tests run.

Let me know if you have any questions!

:octocat: