added special syntax to reason about the return value of methods in the post condition, added some equivalent mutants (c# code), changed while loops to generate smaller wlp formulas if the loop does not affect the post condition

WLP is now calculated for every method seperately, instead of just for the main method. The code for filling the type environment is now seperated from the rest of the program.

break and continu fixed and tested. Added a settings file with an optional invariant for testing loops. Fixed a bug with the call to the verifier when dealing with loops.