Add `--nul-output|-0` flag to separate element with NUL character (#1550)

This is to ensure solid parsing of complex data (with any binary
content except NUL chars) by separating the `yq` root collection
member's output with NUL char. As a safe-guard, an error will be cast
if trying to use NUL character with content that contains itself NUL
characters inside.

cmd/constant.go

@@ -18,6 +18,7 @@ var colorsEnabled = false
 var indent = 2
 var noDocSeparators = false
 var nullInput = false
+var nulSepOutput = false
 var verbose = false
 var version = false
 var prettyPrint = false