F/ordered autoload

[nuchs]

Hi there, this is a pull request for the issue I raised. This should allow users to specify mutliple auotload options and on startup each will be tried in order until one succeds.

I had considered adding a new startup option that looked to see if the current directory had a session associated with it and if not use the last session but I saw someone else had submitted a pull request for git sessions and I thought a list of options would be more compatible with that.

I've not really done any work with lua before so apologies if it is a little un-idiomatic, I'm happy to tidy it up however you like

I've alos tried to make it so the change won't break any existing configurations

[Shatur]

Almost there. Left a few more suggestions.

[nuchs]

I've updated the formatting and docs as asked, the only thing I was a little unsure about was what you meant by the function docs. Did you mean the comments above the functions, the notes in the readme (both of which I think I've done) or something else?

[Shatur]

Exactly what I meant, thank you!