o Make lltok an abstract type, a pointer to structure instead of a plain

o Make lltok an abstract type, a pointer to structure instead of a plain
  struct.  There are still some memory leaks in the parser --- all
  tokens should be deallocated.

o Added messagestream, warningstream and errorstream control flags so
  each type of message can be directed to a different stream:
     messagestreamstdout
     messagestreamstderr
     messagestream <file>