Added a feature to save frame data

[haji-ali]

For your consideration, I implemented a feature to save the frame data for any frame type, such that the frame becomes persistent (saving tabs and windows across invocations).

[alphapapa]

Hi,

This is an interesting idea, but given that I've already written https://github.com/alphapapa/burly.el and https://github.com/alphapapa/activities.el, which do this outside of Yequake, I'd be reluctant to add a third implementation of essentially the same functionality to another library of mine, especially considering the complexities involved (e.g. I'd rather have to fix issues in as few implementations as possible).

I think it would probably be better to either add some kind of integration with Burly and/or Activities, or document how the user can call Burly/Activities functions in a Yequake frame configuration to do the same thing.

What do you think?

Thanks.

[haji-ali]

Definitely better to integrate/use existing libraries (I didn't know of your burly and activities). I will need some time to figure out how to do what I want in activities for example.

Yequake might also need to add a few hooks to call activities-define, activities-suspend and activities-resume (I guess). One thing I was also unsure about (design-wise) is if buffer-fns should be called again when the frame is restored.

Edit: Just realized that this PR might also be related to #17

[alphapapa]

Thanks. And, yes, #17 would probably be a good option to have as well as some kind of integration with Activities. Feel free to open issues here or on Activities' repo to discuss changes needed to integrate them.