Various small changes.
* Define the standard strict order on pre orders. * Prove that this strict order is well founded for finite sets and finite maps. We also provide some utilities to compute with well founded recursion. * Improve the "simplify_option_equality" tactic to handle more cases. * Axiomatize finiteness of finite maps by translation to lists, instead of by them having a finite domain. * Prove many additional properties of finite maps. * Add many functions and theorems on lists, including: permutations, resize, filter, ...