A grammar for a prolog-like language

Add a new grammar with its parser for the formulas you put with the arcs of the
graph.

The langage is prolog-like (but not exactly prolog).
Make superclass call operations + correction

- Make the BinaryOperator class call a method named operation
determining which operation we are currently evaluating
when the value method is called instead of implementing the
same method in each subclass except for the operation symbol.

- Make the Litteral class differ variables and non variables litterals
Corrections and improvements

Correct some methods bugging (due to lack of tests) like
__str__ or

Improve the NamedExpression eval method by iterating two lists
with zip instead of 'for i in xrange...'

Add new method to return a Property or an Event where variables
are replaced by their evaluation.

Make rand see the difference when the probability of randomness
is given by a variable
A grammar to parse consequences of a transition
Main class to run a state machine graph

Implements how the graph evolved with the properties and events
at each frame.
New menu