[FD] performance improvement ideas

[pvdz]

• Idea: Address two major indexOf performance issues
• Idea: Reduce GC pressure by representing domains more memory efficient
• Idea: implement cycle cutting
• Idea: Optimize markov legends/vectors
• Idea: Don't add solved vars to the var-to-propagators hash
• Idea: Optimize operations on bools
• Idea: More optimizations at compile time
• Idea: variables whose constraints have been eliminated should not actively be solved
• Idea: Improve memory behavior of tracking changed vars during propagation
• Idea: Value distributor that aims to solve/reject a propagator
• Idea: Postpone or eliminate isSolved checks during propagation
• Idea: Var distributor that is based on most constraints affected
• Idea: Introduce a conditional that can prune constraints/vars
• Idea: Precompute var distributions
• Idea: Precompute value distributions
• Idea: Boolean specific reifiers
• Idea: Pre-optimize distinct by pruning solved vars
• Idea: Try to implement asm.js
• Idea: Implement fd in webassembly
• Idea: Prune values from a domain that are not in a list distributor's list
• Idea: Prune useless reifiers
• Idea: Trie optimizations