Add PhpDoc block to help IDE completion

Update badges

Fix bug when calling get() twice with non existing key

Fix exception message

Allow '0' or 0 id

::get() now take a flag as second parameter to force empty instance w…

…hen no result (instead of null)

Fix error when converting empty value to id. Now return null

Update tests

Fix getAll returns an array with 'not-exist' id if get('not-exist') i…

…s called before

Rename "Builder" to "Manager"