Improve warnings around Text::uuid()
Improve warnings around Text::uuid()

This function should not be used to generate 'secure' identifiers. While
UUID v4 has a low chance of collisions it is not as foolproof as 64
fully random bytes.

I've also opted to use a more secure source of random integers in PHP7
as mersenne twister to reduce the risk of if these uuids are used in
a security related context.

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