… and *

- add new lexical symbols for <- and <->
- reshape the pgq.y grammar rules to use these

now, we allow them

so the <-> and <- symbols were removed again.

This change of thought was triggered by the mayhem the new lexical
symbols were causing:

================================================================================
Query unexpectedly failed (test/optimizer/move_constants.test:101)
================================================================================
EXPLAIN SELECT -1*X<-5 FROM test;
================================================================================
Actual result:
Parser Error: syntax error at or near "<-"
LINE 1: EXPLAIN SELECT -1*X<-5 FROM test

but the main result of this PR is still: you can now type ->* without spaces