Generalize variables stored during CI builds

[agitter]

Currently, Manubot stores the repository and commit metadata when it is run on Travis CI:

manubot/manubot/process/util.py

Lines 189 to 199 in 66c1c87

	# Set repository version metadata for Travis CI builds only
	# https://docs.travis-ci.com/user/environment-variables/
	if os.getenv('TRAVIS', 'false') == 'true':
	repo_slug = os.environ['TRAVIS_REPO_SLUG']
	repo_owner, repo_name = repo_slug.split('/')
	variables['ci_source'] = {
	'repo_slug': repo_slug,
	'repo_owner': repo_owner,
	'repo_name': repo_name,
	'commit': os.environ['TRAVIS_COMMIT'],
	}

Per manubot/rootstock#198 (comment) we would like to generalize this to store similar metadata for other continuous integration services. AppVeyor is of immediate interest because it will be used for pull request build previews in manubot/rootstock#262.

AppVeyor's environment variables are listed at https://www.appveyor.com/docs/environment-variables/. We likely want:

• APPVEYOR
• APPVEYOR_PROJECT_SLUG
• APPVEYOR_REPO_COMMIT

We could also store which CI service was used in a new variable. When updating manubot/rootstock, we'll also need to update the front matter permalink, which is only relevant for Travis CI.

[dhimmel]

I will work on the implementation of this

we'll also need to update the front matter permalink, which is only relevant for Travis CI.

Currently, 00.front-matter.md contains:

{% if ci_source is defined -%}
([permalink](https://{{ci_source.repo_owner}}.github.io/{{ci_source.repo_name}}/v/{{ci_source.commit}}/))
{% endif -%}

So do we want to omit the permalink altogether for AppVeyor builds or do we want to give the artifact link?

[agitter]

I hadn't thought about giving the artifact link. I like that idea. The artifacts aren't permanent though, so it would be a slight abuse of terminology to call it a permalink (even though AppVeyor does in their webhook doc).

I'm also okay discarding the link completely if that's easier. Or adding a new ci_source.deploy flag to indicate whether we want to display the link.