add/mod the following features

- split structure for better inclusions
- create PlainRenderer to render contents to the terminal
- simplify events
- clearify what structs are created on the heap and which are on the stack
- quit event is now emitted from the main event loop and not the input loop (see helper function `App.quit`)
- rename several variables and/or functions for easier understanding
- introduce `App.interrupt` to stop the input thread and start a new sub TUI which takes over the entire screen (i.e. 'hx', 'nvim', etc.)

src/layout/Pane.zig

@@ -1,4 +1,5 @@
 const std = @import("std");
+const terminal = @import("../terminal.zig");
 const isTaggedUnion = @import("../event.zig").isTaggedUnion;
 const Error = @import("../event.zig").Error;
 
@@ -11,6 +12,7 @@ pub fn Layout(comptime Event: type) type {
         widget: Widget = undefined,
         events: std.ArrayList(Event) = undefined,
         c: std.ArrayList(u8) = undefined,
+        size: terminal.Size = undefined,
 
         pub fn init(allocator: std.mem.Allocator, widget: Widget) @This() {
             return .{
@@ -28,6 +30,12 @@ pub fn Layout(comptime Event: type) type {
         }
 
         pub fn handle(this: *@This(), event: Event) !*std.ArrayList(Event) {
+            switch (event) {
+                .resize => |size| {
+                    this.size = size;
+                },
+                else => {},
+            }
             this.events.clearRetainingCapacity();
             if (this.widget.handle(event)) |e| {
                 try this.events.append(e);