Correct setting position of stringized tokens

Symbols that are created from tokens that come from the use of the stringize
operator ('#') in a macro definition have accurate approximation of their
position. Moreover, some new tests for tokens positions are added.
Add macro tokens to the multimap in ParseExecutor

Macro tokens are added to the tokens multimap in class:
   pl.edu.mimuw.nesc.ParseExecutor.ParseFileExecutor