Date Operators

[clinejm]

Have the ability to compare date fields:

• before { field: 'start_date', operator: 'is_before', value: {date: 'now'} }
• after { field: 'end_date', operator: 'is_after', value: {date: 'now'} }
• between (spec TODO)
• absolute dates (spec TODO what date formats/libraries to use)
• relative dates (spec TODO)