code: func NewRegexpFakeTransport(allMatchers []*Matcher) (http.RoundTripper, error) {
  	var result regexpFakeTransport = []*regexPair{}
  	for _, matcher := range allMatchers {
  		r, err := regexp.Compile(matcher.URLRegex)
  		if err != nil {
  			return nil, err
  		}
  		pair := regexPair{r, matcher.Fn}
  		result = append(result, &pair)
  	}
  	return result, nil
  }
docs: // NewRegexpFakeTransport takes a slice of Matchers and returns an
  // http.RoundTripper that will apply the function associated with the
  // first UrlRegex that matches.