Resolve image undefined

Currently, calling `Faker.Image` with the current implementation results in the following error:
![faker error](http://puu.sh/8xUji.png)

I've also improved the test coverage for the `Image` module from ~60% to 100%.

Running `make build` changed a lot of files I do not feel comfortable committing (removal of gender generation and some random README text). However, I did notice that all the built files are being included. Please advise.