Fix the deploy_folder fallbacks and the docstring for deploy_folder

[DilumAluthge]

No description provided.

[DilumAluthge]

@mortenpi @fredrikekre I think this should fix the deploy_docs stuff and the docstrings that Fredrik mentioned.

[DilumAluthge]

I tried to add a docstring for DeployDecision. But this broke LinkCheck. When I removed the docstring for DeployDecision, then LinkCheck passed.

This is the docstring I tried to add:

"""
    DeployDecision(; kwargs...)
Struct containing information about the decision to deploy or not deploy.
# Arguments
- `all_ok::Bool` - Should documentation be deployed?
- `branch::String` - The branch to which documentation should be pushed
- `is_preview::Bool` - Is this documentation build a pull request?
- `repo::String` - The repo to which documentation should be pushed
- `subfolder::String` - The subfolder to which documentation should be pushed
"""

[mortenpi]

I re-added the docstring, let's see what happens. I don't see anything in it that should cause linkcheck to fail. However, Travis and AppVeyor tests were both failing too, without the docstring.

[DilumAluthge]

All right I think I should've fixed the tests now.

[DilumAluthge]

Okay, CI is passing now.

[DilumAluthge]

@mortenpi @fredrikekre Anything else I should add to this PR?