Fix encoding/decoding issue of UserInfo

[safareli]

Before this PR one couldn't use : or @ in username or password now it's possible.

To achieve this representation of UserInfo changed to record instead of just string as we need to encode username and password separately (without "connecting" :)

[safareli]

This issue raised when @ was part of the username for mongo connection url. Here I see that username and password are passed through decodeURIComponent http://mongodb.github.io/node-mongodb-native/2.2/tutorials/connect/authenticating/.

I adopted the encoding part from go as it's most straight forward, the one from node is way to cryptic
https://github.com/nodejs/node/blob/e22b8d0c46728ebdaf64176191ffa2bdd0f56be9/lib/url.js#L972

[garyb]

The problem with this approach is it assumes the userinfo stuff has a particular structure, which is not necessarily the case - what we have here is the most common case, but according to the spec, the format in there has no specific grammar (aside from the allowable characters).

There is some problem here though, probably just we should do percent encode/decode, since the grammar is:

userinfo    = *( unreserved / pct-encoded / sub-delims / ":" )

[safareli]

will be fixed in #43