Document recommended Travis CI configuration

[dbarnett]

Vim plugins on github can get easy, free continuous integration running vroom in Travis CI.

Once we settle some of the details in our Travis CI configuration and get neovim mode working (#64), we should add a section to the README about how to configure Travis CI to test vim plugins using vroom, and different options you might want to use for your project.

[dbarnett]

Ideally travis-ci/travis-ci#2877 is implemented first, since the vim and neovim modes have different dependencies and the current approach is cumbersome. We can document the best we have in the meantime, though.

[dbarnett]

I documented the basics. We should add documentation for neovim after we finalize some details (and set it up for maktaba and glaive to make sure it works well there).

And if Travis CI implements independent job configurations any time soon, we should definitely clean up the $CI_TARGET workaround and recommend the simpler alternative.

[suoto]

(I've been running CI on a Vim plugin using Travis CI and recently started using Vroom, which is running very nice so far.)

One thing I noticed is that Travis log gets all messed up by Vim trying to draw on stdout, but vroom's help says to avoid shell redirection. You can check this build if you are not already aware of this.

So the question is: is there a (undocumented?) way of avoiding this so Travis log remains "sane"?

[dbarnett]

Vim behavior relies heavily on ncurses (the console UI library) being able to communicate with a real terminal. The shell output is annoying sometimes but not easily fixable.

[dbarnett]

Also note: vroom is using the legacy Travis mode with sudo: false, and until we update our tests to fetch prebuilt binaries, vroom users won't have an easy way to do it either and will be pretty much stuck not being able to use Travis's new container-based system.