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).

build.zig

@@ -18,14 +18,14 @@ pub fn build(b: *std.Build) void {
     lib.addImport("code_point", zg.module("code_point"));
 
     // TODO: examples (not yet available)
-    // const stack_example = b.addExecutable(.{
-    //     .name = "stack",
-    //     .root_source_file = b.path("examples/stack.zig"),
-    //     .target = target,
-    //     .optimize = optimize,
-    // });
-    // stack_example.root_module.addImport("zterm", lib);
-    // b.installArtifact(stack_example);
+    const container = b.addExecutable(.{
+        .name = "container",
+        .root_source_file = b.path("examples/container.zig"),
+        .target = target,
+        .optimize = optimize,
+    });
+    container.root_module.addImport("zterm", lib);
+    b.installArtifact(container);
 
     // testing
     const lib_unit_tests = b.addTest(.{