ogma-language-cocospec: Add unary operators ZtoPre, YtoPre. Refs #86.

Ogma cannot handle CoCoSpec boolean specifications containing the unary
operators ZtoPre or YtoPre. This makes some of the specifications produced by
FRET not parseable.

This commit modifies the CoCoSpec grammar to include two new unary operators:
ZtoPre and YtoPre.

ogma-language-cocospec/grammar/CoCoSpec.cf

@@ -49,12 +49,14 @@ BoolSpecOp2ST.  BoolSpec ::= "ST" "(" NumExpr "," NumExpr "," BoolSpec "," BoolS
 
 -- Boolean Operators
 
-Op1Once.   Op1Pre ::= "O"   ;
-Op1Pre.    Op1Pre ::= "pre" ;
-Op1Hist.   Op1Pre ::= "H"   ;
-Op1Y.      Op1Pre ::= "Y"   ;
-Op1Not.    Op1Pre ::= "not" ;
-Op1Bang.   Op1Pre ::= "!"   ;
+Op1Once.   Op1Pre ::= "O"      ;
+Op1Pre.    Op1Pre ::= "pre"    ;
+Op1YtoPre. Op1Pre ::= "YtoPre" ;
+Op1ZtoPre. Op1Pre ::= "ZtoPre" ;
+Op1Hist.   Op1Pre ::= "H"      ;
+Op1Y.      Op1Pre ::= "Y"      ;
+Op1Not.    Op1Pre ::= "not"    ;
+Op1Bang.   Op1Pre ::= "!"      ;
 
 Op2And.     Op2In ::= "and"     ;
 Op2Amp.     Op2In ::= "&"       ;