Add struct and type doc comments for extra::url::*

[dhodder]

No description provided.

[huonw]

Is this the user part of https://user@example.com:8080/foo/bar?baz=qux#quz? (It would be neat if this had an example URL (e.g. the one I just gave, assuming it covers everything) in the main heading on the struct itself, and then the documentation on each field referred back to the appropriate part so it was unambiguous.)

[dhodder]

It is indeed the user part. Does the following look okay to you? I've added an example URL and updated the descriptions on the individual attributes.

/// A Uniform Resource Locator (URL).  A URL is a form of URI (Uniform Resource
/// Identifier) that includes network location information, such as hostname or
/// port number.
///
/// # Example
///
/// ```rust
/// let url = Url { scheme: ~"https",
///                 user: Some(UserInfo { user: ~"username", pass: None }),
///                 host: ~"example.com",
///                 port: Some(~"8080"),
///                 path: ~"/foo/bar",
///                 query: ~[(~"baz", ~"qux")],
///                 fragment: Some(~"quz") };
/// // https://username@example.com:8080/foo/bar?baz=qux#quz
/// ```
#[deriving(Clone, Eq)]
pub struct Url {
    /// The scheme part of a URL, such as `https` in the above example.
    scheme: ~str,
    /// A URL subcomponent for user authentication.
    /// `Some(UserInfo { user: ~"username", pass: None })` in the example above.
    user: Option<UserInfo>,
    /// A domain name or IP address.  For example, `example.com`.
    host: ~str,
    /// A TCP port number, for example `8080`.
    port: Option<~str>,
    /// The path component of a URL, for example `/foo/bar`.
    path: ~str,
    /// The query component of a URL.  `~[(~"baz", ~"qux")]` represents the
    /// fragment `baz=qux` in the above example.
    query: Query,
    /// The fragment component, such as `quz`.  Does not include the leading hash or pound sign.
    fragment: Option<~str>
}

Thanks!

[huonw]

I think the user part should say just "username in the above example" rather than using the Rust struct syntax. Also choose one for "hash or pound sign" (you could even write "doesn't include the leading #"), at the moment it could be interpreted as "doesn't include the leading hash, and also doesn't include the leading pound sign" which is nonsensical but may be confusing to a nonnative speaker.