Add Travis CI config to release built HTML book on tag

[louy2]

I think it is convenient to have an offline version of the book for download as well, so I wrote this Travis CI config to do that. With it Travis CI can take care of releasing a zip archive of the HTML book on tag. Creating a release on Github also triggers it to append the archive to the release.

Of course, you need to go to Travis CI to enable it for this repo. It also requires env var GH_DEPLOY_TOKEN be filled with a Github personal access token with "public_repo" enabled. This can be set in the Settings tab in the Travis CI page of this repo.

[louy2]

An example build.

[edunham]

@louy2 Thank you!

Following https://twitter.com/Gankro/status/759861678863372288, I'm currently working with the various rust-* GitHub organizations to see what org it would be most appropriate to maintain this repo in long-term. Once it lands in an org (hopefully within the next day or two), I'll set up Travis and get your changes merged!

[louy2]

@edunham Thanks for taking up the maintenance!

I need to change the script a bit to zip the upper folder in as well, otherwise code highlighting doesn't work and redundant code can be seen. So please wait a bit till then to merge.

[edunham]

@louy2 And we've landed! Travis is now enabled on this repo.

I'd like to land your .travis.yml pretty soon so that we can start adding lints without conflicting against this PR, and actually testing PRs :)

[louy2]

I am sorry for the delay! The released zip now contains the necessary rust.css to be displayed normally. It is ready for merge.

[edunham]

Thank you so much for all the work on this!