#87 - Allow static macros

[Luke-Shepp]

Fixes: #87

Money and Currency override the Macroable __callStatic method, effectively disabling static macros.

To resolve this issue, a check has been added: If the statically called method exists as a macro, then call the macro instead.

Additionally, added Macros and Mixins to the README - currently this functionality is not documented.

Tests:

Example usage:

use Akaunting\Money\Currency;
use Akaunting\Money\Money;

Money::macro(
    'zero', 
    fn (?string $currency = null) => new Money(0, new Currency($currency ?? 'GBP'))
);

$money = Money::zero();

[denisdulici]

Thanks for your contribution.