add(examples/demo): application to showcase a more complex application

Further improvements for example applications; Demo example is now
default build target (when not providing example configuration).

build.zig

@@ -5,6 +5,7 @@ pub fn build(b: *std.Build) void {
     const optimize = b.standardOptimizeOption(.{});
 
     const Examples = enum {
+        demo,
         // elements:
         button,
         input,
@@ -21,7 +22,7 @@ pub fn build(b: *std.Build) void {
         errors,
     };
 
-    const example = b.option(Examples, "example", "Example to build and/or run. (default: vertical)") orelse .vertical;
+    const example = b.option(Examples, "example", "Example to build and/or run. (default: demo)") orelse .demo;
 
     const options = b.addOptions();
     options.addOption(Examples, "example", example);
@@ -42,6 +43,15 @@ pub fn build(b: *std.Build) void {
 
     //--- Examples ---
 
+    // demo:
+    const demo = b.addExecutable(.{
+        .name = "demo",
+        .root_source_file = b.path("examples/demo.zig"),
+        .target = target,
+        .optimize = optimize,
+    });
+    demo.root_module.addImport("zterm", lib);
+
     // elements:
     const button = b.addExecutable(.{
         .name = "button",
@@ -128,6 +138,7 @@ pub fn build(b: *std.Build) void {
 
     // mapping of user selected example to compile step
     const exe = switch (example) {
+        .demo => demo,
         // elements:
         .button => button,
         .input => input,