Added a note to the README file
Simplify data model for snapshots

Now, when a value is not "complicated" such as an Array or an
Object, it is not converted to a Snapshot object, but left as is
Fix .gitignore for docs build path
Continue previous simplification

Rename again Snapshot to AbstractSnapshot, as it is not used
anymore and not destined to be used anymore
Delete deep snapshots handling to AbstractSnapshot
Set isComparable to public instead of protected
First step towards more detailed changed
Add class AbstractChange and remove interface ChangeInterface
Rewrite top condition in the Set::compute method
Remove useless condition in the Set::compute method
Add detections on removal / additions in Set::compute
Remove the ArraySnapshot isComparable method

Let the parent isComparable do the work
Release 1.2.0