CI job to build / host docs

[MylesBorins]

When people submit changes such as nodejs/node#6100 for broken links it would be really great if we could run a CI job to quickly build the docs and host them. This would speed up the process of multiple reviewers, and allow people to review without having to build the docs locally

[stevemao]

In my own repo, https://github.com/stevemao/awesome-git-addons, there are two bots hit me:

• https://github.com/dkhamsing/awesome_bot
• https://github.com/dkhamsing/frankenstein

issues:

• Validate pull requests with Travis stevemao/awesome-git-addons#5
• Update redirects in Readme stevemao/awesome-git-addons#4

frankenstein can open a pull request to update README links based on HTTP redirects
awesome_bot checks for valid URLs in a file, it can be used to verify pull requests updating a README.

Should be easy to be integrated with our existing CI.

[kahwee]

Is this a generic bot to build docs rather than just for checking if the links are valid?