Clarify details for the execution environment for actions (#531)
Clarify details for the execution environment for actions (#531)

* Clarify execution environment of actions and predicates
* Makes a new section for describing the common execution environment
* Add the new section to TOC
* Clarify start/end for predicates
* Clarify the scope of labels

pegjs/pegjs,Mingun/pegjs,pegjs/pegjs,Mingun/pegjs