Support for uploading documentation to ghp

[epage]

@jonhoo in #23

There are a number of other GitHub artefacts we may also want to produce. Two good examples are pushing master documentation to gh-pages and producing GitHub releases. There is some more context over at tokio-rs/tracing#191 (comment).

[epage]

For uploading as part of a pipeline, cargo-ghp-upload might be able to help.

An alternative is to instead upload when cutting a release using cargo-release

[jonhoo]

I think this is now explicitly out-of-scope. If your project wants this, it should write a job that uses the install-rust template and then builds the necessary resources.

[jonhoo]

See also #78.