loader: Make LoaderOptions a builder style struct

To pave the way for future loader options without
having public fields all the time causing major version jumps,
we are taking the hit now to hide the fields and expose methods
for the various loader options.

Signed-off-by: Daniel Silverstone <dsilvers@digital-scurf.org>

marked-yaml/src/loader.rs

@@ -40,11 +40,26 @@ pub enum LoadError {
 }
 
 /// Options for loading YAML
+///
+/// Default options ([`LoaderOptions::default()`]) are:
+///
+/// - Permit duplicate keys
+///
 #[derive(Debug, Default)]
 pub struct LoaderOptions {
-    /// If true, duplicate keys in mappings will cause an error. If false,
-    /// the last key will be used.
-    pub error_on_duplicate_keys: bool,
+    error_on_duplicate_keys: bool,
+}
+
+impl LoaderOptions {
+    /// Enable errors on duplicate keys
+    ///
+    /// If enabled, duplicate keys in mappings will cause an error.
+    /// If disabled, the last key/value pair will be used.
+    pub fn error_on_duplicate_keys(self, enable: bool) -> Self {
+        Self {
+            error_on_duplicate_keys: enable,
+        }
+    }
 }
 
 impl Display for LoadError {