Refactored decoder responsibilities (#1402)

- improved comment handling
- yaml decoder now responsible for leading content work around

pkg/yqlib/yaml.go

@@ -0,0 +1,19 @@
+package yqlib
+
+type YamlPreferences struct {
+	LeadingContentPreProcessing bool
+	PrintDocSeparators          bool
+	UnwrapScalar                bool
+	EvaluateTogether            bool
+}
+
+func NewDefaultYamlPreferences() YamlPreferences {
+	return YamlPreferences{
+		LeadingContentPreProcessing: true,
+		PrintDocSeparators:          true,
+		UnwrapScalar:                true,
+		EvaluateTogether:            false,
+	}
+}
+
+var ConfiguredYamlPreferences = NewDefaultYamlPreferences()