fixed syntax of command set-option according to SMT-LIB2 standard
registered names of cardinality tags in SMT_Tag_Mapping
allow SimpleSymbolTable to use unanmed, internal variables (e.g., cardinality)
implemented SetOption command in SMT-LIB2 parser
inserted cardinality tags to all_Tags
implemented support for cardinality logic in SMT-LIB2 parser
added missing default impl (BDD) for card_eq
Fixed  arity problem with left-associative tags

The problem was that smt constraints such as "(assert (or/and x))" resulted in an error
as there was an assertion that the amount of arguments must at least be 2.

This assertion is removed. The solution is just to evaluate the argument, changing
(assert (or/and x)) to (assert (x)). This seems to be a reasonable assumption.
Server ignores comments in smt input

Until now in case of a comment line the message
  ERROR: Parsing failed!
  Stop at: <comment>
was printed. This is removed
removed unneccessary debug output
Added debug output in case of unfound variable

Until now only an assertion without any hint about the variable in question showed up.
Now the additional output
	Could not determine variable: <varname>
is sent to std::cerr.
removed unused connection.hpp file
Added safety check for (get-value)

In case of UNSAT, calling get-value resulted in
* assignment of FALSE to requested variable (SMT2)
* crash (Z3)

Both behaviours are, obviously, wrong. The server now ignores
calls to get-value if the most recent check-sat did not result
in SAT. If check-sat wasn't called when asking for a value,
the get-value command is also ignored.