Array entry token and shortcuts to match entry, key or value

Token comes with 3 shortcuts:
* ```Argument::withEntry($key, $value)``` to check if array contains (key, value) pair. 
* ```Argument::withKey($key)``` to check if array contains key
* ```Argument::containing($value)``` to check if array contains value

Both ```$key``` and ```$value``` can be either exact values or tokens. 
It only scores when both ```$key``` and ```$value``` score at least one same entry in the array. 
The most debatable part is how to score matched entries. I ended up choosing to calculate it as ```(key_score + value_score) / 2``` and cap it at 8.  It takes both tokens into account and should keep fair priorities.