Allow string as input for useSymbols

[princejohnsantillan]

This allows defining symbols list as a string instead of an array. Makes for better DX.

Example:

Random::useSymbols("A1B2C3D4")->string();

[valorin]

I love the idea, can you expand it for the other use*() methods?
Also, some tests would be great.

One problem, you can't use array|string with the PHP 7,x versions. Check the failing tests. 🙂

[valorin]

Awesome, thanks!