feat(display): add methods to display

- Add `indent`, `faint`, and `underline` methods to `display`
- Add tests for the above

internal/display/faint_test.go

@@ -0,0 +1,14 @@
+package display
+
+import (
+	"testing"
+)
+
+// TestFaint asserts that Faint applies faint formatting
+func TestFaint(t *testing.T) {
+	want := "\033[2mfoo\033[0m"
+	got := Faint("foo")
+	if want != got {
+		t.Errorf("failed to faint: want: %s, got: %s", want, got)
+	}
+}