Test encoding of URL params

[angrynode]

Apparently Url::parse and Url::parse_with_params do different things leading to a different encoding and therefore string rep.

In Url::parse, : is preserved across params. That's not the case when using parse_with_params which internally uses query_pairs_mut.

I'm not sure which is correct in the general case. If i understand RFC 3986 they should be encoded in all cases, except when the protocol specifies it.

This PR only contains tests as i'm not familiar with url crate internals.

[Manishearth]

I'm not sure which is correct in the general case. If i understand RFC 3986 they should be encoded in all cases, except when the protocol specifies it.

n.b. this crate implements https://url.spec.whatwg.org/ not RFC 3986

[angrynode]

@Manishearth If magnet links are not supposed to be supported feel free to close this PR and i'll open one to write supported schemes in the README. I'm not sure how RFC and WhatWG differ. I see in the spec you linked there is a mailto: example but i don't see much about non-HTTP schemes in general.

[Manishearth]

I think magnet links should be supported. I'm just saying that you're looking at the wrong standard