feat(display): add methods to display

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

internal/display/indent.go

@@ -0,0 +1,16 @@
+package display
+
+import (
+	"fmt"
+	"strings"
+)
+
+// Indent prepends each line of a string with a tab
+func Indent(str string) string {
+	out := ""
+	for _, line := range strings.Split(str, "\n") {
+		out += fmt.Sprintf("\t%s\n", line)
+	}
+
+	return strings.TrimSuffix(out, "\n")
+}