In memory db

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My attempt at #547

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You'll notice:

https://github.com/openmultiplayer/open.mp/pull/553/files#diff-ae0442be1191ac118f27664b290559d196c369fd5c373b25a40b587ad3d8a16cR69-R73

Whether that's uncommented or not will determine a lot in terms of what semantics we want to allow. Should people be able to access other places on the disk? That somewhat defeats the purpose of scriptfiles/ as a sandbox.

[Y-Less]

In response to @AmyrAhmady:

The reason I didn't go that way to support all possible in-memory database methods, is to support opening databases in a more standard way, support everything and not just absolute DB path on disk
https://www.sqlite.org/c3ref/open.html#urifilenameexamples
https://www.sqlite.org/inmemorydb.html

The commented out bit will allow any path, the rest of the code covers even more in-memory creation methods than yours had.