Add UUID support for _id field

[altaraven]

Please make it possible to use UUID as primary key. For example, doctrine can do this via annotations

/** @Id(strategy="UUID", type="string") */
private $id;

[mfauveau]

Hi @altaraven,

I made some modifications to be able to do just that. See this PR #1611.

[altaraven]

Hello @mfauveau. Yes, I saw your PR. I just hope that package author will accept it or write his own. I also didn't get why you used Binary and not simple string

[Smolevich]

@altaraven, jenssegers/laravel-mongodb-core#1

[divine]

Closing, merged in #1611