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).

src/cell.zig

@@ -3,7 +3,7 @@ const Style = @import("style.zig");
 
 pub const Cell = @This();
 
-style: Style = .{ .attributes = &.{} },
+style: Style = .{ .emphasis = &.{} },
 // TODO: embrace `zg` dependency more due to utf-8 encoding
 cp: u21 = ' ',
 
@@ -12,7 +12,7 @@ pub fn eql(this: Cell, other: Cell) bool {
 }
 
 pub fn reset(this: *Cell) void {
-    this.style = .{ .attributes = &.{} };
+    this.style = .{ .emphasis = &.{} };
     this.cp = ' ';
 }