Weighted grammars

[IssaHanou]

Add the possibility of assigning different weights (costs) to the rules of a grammar. The setup should be similar to the probabilistic_csg. The costs should be used in evaluating a program, such that expensive rules should be minimized in use.

Requirements:

• The default should be 0 for a rule.
• Grammars should be possible to use both probabilities and weights
• We want to do search with a budget (handle in constraint solver)
  • uniform tree that violates the budget should be discarded
  • budget is local
• Only non-negative weights

The creation of the grammar type and the use in the iterators can be split into different PRs

Extensions:

• toy example
• search that uses weights