allow visitors to use markable

[atmonshi]

is it possible to allow guests none logged in users to add (like) or any other bookmark?

I know it's currently not :) since the user_id don't accept nulls. but can you think of any issues down the road, and will you open to PR?

thank you all.

[atmonshi]

its similar to #9

my use case is to allow visitors to (like) a post, which is important to get accurate number of (liked) posts.

[atmonshi]

I tried the suggestion: Create a user called guest

but markable uses firstOrCreate to add a mark, so the "guest" user cant (like) the same post.

maybe adding a new flag force? and it always create a new record.

Like::add($this, $user, force:true)