Regenerate documentation and add support for untrusted root

[m8rmclaren]

Added caCertificates []*x509.Certificate to Configuration struct and associated setter for Configuration promoted method.

func (c *Configuration) SetCaCertificates(caCertificates []*x509.Certificate) {
	if caCertificates != nil {
		c.caCertificates = caCertificates
	}
}

Then, built func buildHttpClient(config *Configuration) (*http.Client, error) function that places the trusted roots in the underlying transport layer.

Finally, updated README.md to detail the new support for setting root CAs.