Add more Debug implementations

I generally like to implement Debug on these kind of types.

src/edit/editor.rs

@@ -16,6 +16,7 @@ use crate::{
 };
 
 /// A wrapper of [`Buffer`] for easy editing
+#[derive(Debug)]
 pub struct Editor {
     buffer: Buffer,
     cursor: Cursor,

src/edit/syntect.rs

@@ -12,6 +12,7 @@ use crate::{
     Shaping, Style, Weight, Wrap,
 };
 
+#[derive(Debug)]
 pub struct SyntaxSystem {
     pub syntax_set: SyntaxSet,
     pub theme_set: ThemeSet,
@@ -29,6 +30,7 @@ impl SyntaxSystem {
 }
 
 /// A wrapper of [`Editor`] with syntax highlighting provided by [`SyntaxSystem`]
+#[derive(Debug)]
 pub struct SyntaxEditor<'a> {
     editor: Editor,
     syntax_system: &'a SyntaxSystem,

src/edit/vi.rs

@@ -16,6 +16,7 @@ enum Mode {
     SearchBackwards,
 }
 
+#[derive(Debug)]
 pub struct ViEditor<'a> {
     editor: SyntaxEditor<'a>,
     mode: Mode,