WIP: add Container type with corresponding Properties configuration

The configuration of the `Container` types is very much inspired by
[clay](https://github.com/nicbarker/clay).

examples/container.zig

@@ -0,0 +1,59 @@
+const std = @import("std");
+const zterm = @import("zterm");
+
+const App = zterm.App(union(enum) {});
+const Key = zterm.Key;
+
+const log = std.log.scoped(.example);
+
+pub fn main() !void {
+    errdefer |err| log.err("Application Error: {any}", .{err});
+
+    var gpa = std.heap.GeneralPurposeAllocator(.{}){};
+    defer {
+        const deinit_status = gpa.deinit();
+        if (deinit_status == .leak) {
+            log.err("memory lead", .{});
+        }
+    }
+    const allocator = gpa.allocator();
+
+    var app: App = .{};
+    var renderer = zterm.Renderer.Buffered.init(allocator);
+    defer renderer.deinit();
+
+    var container = try App.Container.init(allocator, .{});
+    defer container.deinit();
+
+    // NOTE: should the min-size here be required?
+    try app.start(null);
+    defer app.stop() catch |err| log.err("Failed to stop application: {any}", .{err});
+
+    // event loop
+    while (true) {
+        const event = app.nextEvent();
+        log.debug("received event: {s}", .{@tagName(event)});
+
+        switch (event) {
+            .init => {
+                if (container.handle(event)) |e| app.postEvent(e);
+                continue;
+            },
+            .quit => break,
+            .resize => |size| try renderer.resize(size),
+            .key => |key| {
+                if (key.matches(.{ .cp = 'q' }))
+                    app.quit();
+            },
+            .err => |err| {
+                log.err("Received {any} with message: {s}", .{ @errorName(err.err), err.msg });
+            },
+            else => {},
+        }
+
+        // TODO: should instead use tryPost because it may block the main loop from actually removing events from the queue, deadlocking itself
+        if (container.handle(event)) |e| app.postEvent(e);
+        renderer.render(@TypeOf(container), &container);
+        try renderer.flush();
+    }
+}