feat: Allow bulk-adding of snippets, footers, annotations

This will make it easier for diagnostic systems to convert their
messages to a `Message`

Author: epage

Diff for: src/snippet.rs

@@ -34,10 +34,20 @@ impl<'a> Message<'a> {
         self
     }
 
+    pub fn snippets(mut self, slice: impl IntoIterator<Item = Snippet<'a>>) -> Self {
+        self.snippets.extend(slice);
+        self
+    }
+
     pub fn footer(mut self, footer: Label<'a>) -> Self {
         self.footer.push(footer);
         self
     }
+
+    pub fn footers(mut self, footer: impl IntoIterator<Item = Label<'a>>) -> Self {
+        self.footer.extend(footer);
+        self
+    }
 }
 
 pub struct Label<'a> {
@@ -116,6 +126,11 @@ impl<'a> Snippet<'a> {
         self
     }
 
+    pub fn annotations(mut self, annotation: impl IntoIterator<Item = Annotation<'a>>) -> Self {
+        self.annotations.extend(annotation);
+        self
+    }
+
     pub fn fold(mut self, fold: bool) -> Self {
         self.fold = fold;
         self