User:
{"username": "fcc_test", "_id": "12345"}
Exercise:
{"username": "fcc_test", "description": "test", "duration": 60, "date": "Mon Jan 01 1990", "_id": "12345"}
Log:
{"username": "fcc_test", "count": 1, "_id": "12345", "log": [{"description": "test", "duration": 60, "date": "Mon Jan 01 1990"}]}