feat: allow colored formatting

[ernado]

Use github.com/fatih/color, highlight error text, stacktrace parts (line number, path to file, stacktrace element) with different colors and bold/faint.

Example of colored formatted string:

fmt.Println(
	color.New(color.FgCyan).Sprintf("[%5s]", time.Since(start).Round(time.Second)),
	color.New().Sprint(req.Method),
	color.New(color.Faint).Sprint(req.URL),
	color.New(color.FgYellow).Sprint(lastStatus),
)

Probably implement it as some variant of %+v formatting (do we support flags in formatting strings here?).