action_ method notation

Previously, DRM was intended only for creating scripts. So methods which dealt with navigating or editing the model began with "m" to distinguish them from actions being added to the script.

With DRM being reintended for more general use and sharing greater API comonality with persistent objects, we need to drop the "m". So to distinguish betwee setting a headline on the model and compiling a set headline action, action compilation methods will now end with "_".