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).

build.zig

@@ -15,6 +15,7 @@ pub fn build(b: *std.Build) void {
         grid,
         mixed,
         // styles:
+        text,
         palette,
     };
 
@@ -106,6 +107,14 @@ pub fn build(b: *std.Build) void {
     });
     palette.root_module.addImport("zterm", lib);
 
+    const text = b.addExecutable(.{
+        .name = "text",
+        .root_source_file = b.path("examples/styles/text.zig"),
+        .target = target,
+        .optimize = optimize,
+    });
+    text.root_module.addImport("zterm", lib);
+
     // mapping of user selected example to compile step
     const exe = switch (example) {
         // elements:
@@ -118,6 +127,7 @@ pub fn build(b: *std.Build) void {
         .grid => grid,
         .mixed => mixed,
         // styles:
+        .text => text,
         .palette => palette,
     };
     b.installArtifact(exe);