Inconsistent docs

[apasel422]

Not sure if this was intentional, but the nightly Travis build generates the docs without the nightly features enabled:

    - cargo doc --no-deps
after_success: |
    [ "$TRAVIS_RUST_VERSION" = nightly ] &&

I don't know if we want to host the stable docs or the nightly docs, but the configuration should be changed to the following, regardless:

    - cargo doc --no-deps $FEATURES

[Gankra]

ah-aaaa right we don't have stability features... I guess I would publish the nightly docs...? Gonna cause confusion though.

[apasel422]

I'll leave it to you to decide, but we should at least build the docs with the correct features. I'll edit the file directly.