Artisan commands for populating hashes of existing models

Added a laravelmodelhash:populate artisan command to 'backfill' existing models.

See the readme for more details on syntax and backfilling all models or one-at-a-time.

DB improvements, increased error checking

Merge pull request #3 from Drewdan/feature/suggestions-for-changes

~ reduces queries required to check hash uniqueness

Added some unit testing, fixed some bugs, styled some code

Merge pull request #2 from adamhopkinson/analysis-D2Yddy

Apply fixes from StyleCI

First public version

1.0.0

Create README.md