implement api.trashed

[AlexanderWillner]

Goal

• As a things-cli user
• I want to look at the trash
• so that I know what was deleted

Suggested approach
In order to achieve this goal I suggest to implement api.trashed

Additional context
testing via https://github.com/thingsapi/things-cli

// @mikez

[mikez]

Some suggestions:

1. Call the API things.trash to keep naming consistent with the Things app.
2. Make it a wrapper around things.tasks() and add a new bool-parameter called trashed to said function.