* keywords are no longer than 20 characters, which is a restriction
cargo imposes
* don't use 'homepage' link in cargo.toml unless the homepage is
non-empty
* Added all publish-results to mark the respective crate version
Related to #46
This also includes documentation to state which methods actually support
media download, and how to achieve that.
Added TODO to not forget we should tell the user how to achieve these
kinds of things.
Fixes#21