add(examples/styles): text and color styling possiblities

This also contains some minor refactoring to improve the readability
and understandability of the library (i.e. renaming of Style.Attributes
to Style.Emphasis).

examples/styles/palette.zig

@@ -63,8 +63,7 @@ pub fn main() !void {
 
     inline for (std.meta.fields(zterm.Color)) |field| {
         if (comptime field.value == 0) continue; // zterm.Color.default == 0 -> skip
-        const color = std.meta.stringToEnum(zterm.Color, field.name).?;
-        try box.append(try App.Container.init(allocator, .{ .rectangle = .{ .fill = color } }, .{}));
+        try box.append(try App.Container.init(allocator, .{ .rectangle = .{ .fill = @enumFromInt(field.value) } }, .{}));
     }
     var scrollable: App.Scrollable = .init(box);
     try container.append(try App.Container.init(allocator, .{}, scrollable.element()));