test: validating JSON files

[johnmcguin]

Why is this change being made?

resolves #78

How is this being accomplished?

1. A module to use, providing Ecto schemaless types for each JSON file
2. assert that each object in the file is a valid?: true Ecto changeset.

Some caveats I wanted to note:

• casting will not catch a typo like "names" instead of "name". It simply won't include those properties in the changes.
• You can perform required validations through the required argument when useing the module. This is the main validation I included and consulted the schemas as to what fields should be required.
• If needed, you can override the validate/1 function in a test file. For example, if you needed or wanted to perform additional validations on the changeset for that particular test file.

[johnmcguin]

woohoo, thanks @danielbergholz ! Happy to find such a cool project to contribute to!