Added c_interface function  vc_parseSMTLIB2Expr to parse smtlib2 string and load the asserts and querie into the solver.

Added c_interface function vc_getQueryStateAsCNF to return the solver query state as a Cnf_Dat_t struct (internal struct of STP)

moved some functionality that was done by the  CNF_PrintBack function into vc_printQueryStateAsCNFToBuffer so its consistent with  vc_getQueryStateAsCNF

README update

See merge request !1

Based on STP version 2.3.3.

This modified version adds the function
vc_printQueryStateAsCNFToBuffer to the c interface.
This function returns a Buffer containing a C-String with
the CNF Representation of the current QeryState