There should be an uri::Builder

Right now the burden of correct percent encoding is entirely on the user. This is completely unnecessary. Only accepting string URI also forces users to concatenate strings to construct an URI, which is bad and inefficient practice that leads to bugs.

Examples

Entirely segmented

Uri::builder()
        .https()    // In mio_httpc I have both https() and set_https(true).
        .host("www.example.com")
        .auth("user name", "my password")
        .port(12345)
        .path_segm("a/")
        .path_segm("b")
        .query("spaced key", "123")
        .query("key", "<>")

Only partly segmented because schemes, hosts and optional ports are not a percent encoding problem and often stored as a fixed string on a client.

Uri::builder()
        .base("https://www.example.com:8080")?
        .path_segm("a/")
        .path_segm("b")
        .query("spaced key", "123")
        .query("key", "<>")

Query and path segments could also be slices.

Uri::builder()
        .base("https://www.example.com:8080")?
        .path(&["a", "b", "c d"])
        .query_pairs(&[("spaced key", "123"),("another","key")])

(edit by Sean)

To track the progress, here's what's done and needs to be done:

• Introduce http::uri::Builder
• Builder::scheme()
• Builder::authority()
• Builder::host()
• Builder::port()
• Builder::path_and_query()
• `Builder::path()
• Builder::query()

Start by reading the existing http::uri::Builder implementation and its completed methods: scheme(), authority(), and path_and_query(). Use the checklist as the scope for the remaining host(), port(), path(), and query() work; done means those builder operations support the URI construction shown in the examples.