Migrate to add algorithms table.
Add devise gem, and install default devise files.

We will use devise to generate Developer model.
Migrate to add developers table via Devise.

* Adds Developer model.
* Updates routes.rb to have devise routes.
Migrate to add training_data_sets.
Add TrainingDataSet model.

I also set up Rails association between Developer and
TrainingDataSet model.
Add Algorithm model.

With this, I also seed the database with our first algorithm: the simple
linear regression.
Add validations at model layer.

* Add validations to TrainingDataSet.
* Add validation to Algorithm.
Add model unit tests.

* Add specs for TrainingDataSet.
* Add specs for Algorithm.
* Add factories.rb to define model directives.
Merge pull request #4 from dman7/add-core-tables-3

Add core tables 3