Fix basic authentication with special characters

[mmatczuk]

We are tempering special characters in basic auth headers.

url.UserInfo encodes special characters with URL encoding, see this example

func TestName(t *testing.T) {
	fmt.Println(url.UserPassword("foo", "!@#$^&*").String())
}
output:
=== RUN   TestName
foo:%21%40%23$%5E&%2A
--- PASS: TestName (0.00s)
PASS

This is not suitable for inclusion in a basic-auth header.
Experiments with FireFox(FF) has show that FF would send the text without encoding, for example

Proxy-Authorization: Basic Zm9vOiFAIyReJio=

base64 -d <<< 'Zm9vOiFAIyReJio='
foo:!@#$^&*

Moreover applying URL unescape on user and password when reading them from command line can cause parsing % as a beginning of an escape sequence.