- implemented the string concatenation operator '..'. This is capable of stringifying all of the common types for output.

- gave OP_CONCAT some sane semantics. The way this was defined, by specifying the source operands as a range of registers instead of a pair like everything else made it completely useless for the task at hand.
- changed formatting for floats to %.5f which for normal output in a game makes more sense. For special cases there should be a special formatting function for ints and floats that can do more specialized conversions.

src/scripting/zscript/zcc_compile.cpp

@@ -2959,8 +2959,8 @@ FxExpression *ZCCCompiler::ConvertNode(ZCC_TreeNode *ast)
 		case PEX_Is:
 			return new FxTypeCheck(left, right);
 
-				// todo: These do not have representations in DECORATE and no implementation exists yet.
 		case PEX_Concat:
+			return new FxConcat(left, right);
 
 		default:
 			I_Error("Binary operator %d not implemented yet", op);