Evernode

- Fix for PyYAML

**Highlights**
- Fix for PyJWT
- Other minor changes

**Highlights**
- Removed `MySQLclient` dependency in favour of `PyMySQL`
- Added ability to not use a database

**Notes**
- Use option `"DISABLE_DATABASE": true` in api config.json

**Highlights**
- Added new `Cron` class to schedule tasks in an asynchronous manner
- Added new `Singleton` class
- Added new dependency `schedule`
- Updated comments
- Updated dev app with Cron class examples

**Notes**
The new Cron class has an attribute called `schedule`, this is an alias for the python library called schedule.
https://github.com/dbader/schedule

To use the new Cron class, just initialize it and add tasks to `schedule` attribute.
Example

def task_callable():
print('Hello World!')

cron = Cron()
cron.schedule.every(10).minutes.do(task_callable)


You can initialize the Cron class throughout the app to add tasks, but recommended to only keep cron tasks to the boot of your application.

**Highlights**
- Added decimal.Decimal support to JSON serialization

**Highlights**
- Fixed a bug that if SQLAlchemy model is deferred json class would not display columns in output. If this object lives in the output for JSON be assume you want the columns to display in the json text output. If model is deferred your columns and values will display as expected.
- Added callback parameter for FormData class, if a aborted response of 400 would be issued a callback is triggered first. This is an optional parameter called `fail_callback` and expects a function/method.