added basic value iteration over continuous state-space + several control option + refactored dfs + added basic continuous-only example1 pddl toy problem

added basic value iteration over continuous state-space + several control option + refactored dfs + added basic continuous-only example1 pddl toy problem
added discrete state hashing scheme + improved dfs using unordered_map, yields much faster exploration
added control of max dfs calls when discovering states prior value iteration
updated header of example1 for value iteration