Trigger the PV read function

[NickeZ]

Currently you need to call two functions to trigger a PV to read:

.read(&timespec, &tmp)
.push(timespec, tmp)

this could be simplified to an trigger function.

This is useful when you have a setter and a getter to some configuration parameter and you want the getter to actually get the value from the hardware after you set the value.

Bikeshed away, I'm not particulary happy about the name trigger.