Improve the closure execution backtracking.

[aitrusgit]

Right now context is part of the result provided by the engine.process method. Such context holds a reference to all the rules that have been evaluated (only rules, not other closure types).

1. Does it make sense to hold reference to ALL closures evaluated? The original reason for not going this way was to prevent very granular closures to flood the execution log. We can prevent that by only adding the closures that have certain special mark in the definition ( having a description? having a name?)

2. In line with that we need to have a way for each rule (or closure) to reference their original definition (so things like, by example, description are not lost)