This commit introduces the sealed `UriPart` marker trait as well as the
implementing `Path` and `Query` marker types, allowing for parts of a
URI to be distinguished at the type level. Consequently, `UriDisplay`
has been parameterized with `P: UriPart`, creating `UriDisplay<Path>`
and `UriDisplay<Query>`. The effect of this change is improved type
safely for URI rendering as well as the ability to omit rendering values
in query parts via `Option` and `Result`.
The `UriDisplay` derive was replaced by `UriDisplayQuery` and
`UriDisplayPath` which derive implementations for `UriDisplay<Path>`
and `UriDisplay<Query>`, respectively.
This commit also works around a rustdoc visibility issue by creating a
hidden `http::private` module.
Finally, this commit also removes the now vestigial use of the
`rustc_private` feature in codegen.
Fixes#827.
Prior to this change, Rocket emitted "white" text in much of its logging
output. On terminals with light backgrounds, the text was nearly
illegible. This PR stops using white coloring altogether, opting instead
to use the terminal's default color albeit with bold styling. On dark
terminals, this will likely be a light color, and on light terminals,
this will likely be a dark color. The end result is that Rocket's
logging output should be readable everywhere.
Resolves#639.
