Add the ability to enable/disable logging based on a sensor value

[gigapod]

Feature

Add the ability to the framework that allows events to be triggered based on a sensor value. This would all be done via the menu / config system.

Example uses:

• Only connect/log outputs if the temperature is less that a value
• Only log if a human presence is detected
• Stop logging if a measure weight exceeds a specific value ...etc

[gigapod]

FWIW - I have a prototype of this working - this branch - that proves the concept.

In the proto:

• Value triggers are hard coded/added to the device driver
• User can set a trigger level (value) and a test condition (>, <, ==, !=)
• Trigger causes an event to fire -- which could be monitored by the logger.

Future

Ideally, the trigger events are dynamically added (have a "add rule* menu item). This is possible with the current prototype as a foundation for this - BUT a persistence scheme for the rules is needed.

Each rule needs:

• Parameter it is attached to - parameter name
• Rule operator - i.e. <, >, ==, !-
• Trigger Value

This could be serialized into a preference string => "[ , , ][...]