Major release: new features; breaking changes

New:

• firstPair, lastPair: equivalent to first and last but returns the key as well
• collect: global function in the BapCat\Collection namespace, alias for new Collection(...)
• join: implodes a collection into a string
• isEmpty: alias for count() === 0
• toArray: use instead of all
• combine: see PHP's array_combine

Changed:

• Deprecated all in favour of toArray
• keys/values now return collections