added zip model and migration
Merge pull request #3 from sgray11/census_data

added zip model and migration
added seeds for zips and changed model to take more arguments
Merge pull request #4 from sgray11/zip_seeds

added seeds for zips and changed model to take more arguments
seeds file is now working, needs to be refactored
refactored seeds file
Merge pull request #5 from sgray11/zip_seeds

created a seeds file for zip code demographics
fixed merge conflicts