Add HTMLGitlab formatter

[rumpelsepp]

Since I want to use "real" rouge for gitlab, we need a proper html
formatter. This pull request adds the needed formatter for gitlab.

See also: gitlabhq/gitlabhq#9341

[rumpelsepp]

A note to the failing test: Ruby 1.9 is no longer alive!
https://www.ruby-lang.org/en/news/2015/02/23/support-for-ruby-1-9-3-has-ended/

[rumpelsepp]

see #269

[jneen]

Hey @rumpelsepp, thanks for the PR! This seems to me like a file whose more appropriate home is within the gitlab project. It's mostly the same as the current Formatters::HTML with a few different design decisions.

The direction I'm going for 2.0 is to encourage people to write their own formatters, by having formatters that are easy to extend or compose. There's a branch called refactor.split-html - do you think you could extend from that instead?

[stanhu]

I like the idea. There are some changes in the GitLab HTML formatter that I would like to add that shouldn't require upgrading the rouge version.

[rumpelsepp]

Alright. So, should I close this?
@stanhu Where do we start with the solution for gitlab?

[stanhu]

@rumpelsepp I'm not the authority of this, but I would propose putting it in lib/rouge/formatters/html_gitlab.rb, much like lib/redcarpet/render/gitlab_html.rb.

[jneen]

Closing this for now. I suggest using refactor.split-html, which will be later merged into master and released. I'm happy to take a look at whatever solution you end up with and make sure the proper extension points are in rouge so you don't have to maintain a lot of copy/pasta.

[rumpelsepp]

Fair enough, thanks!