Add way to toggle replaceFirst per plugin/globally

[Phoenix616]

Is your feature request related to a problem? Please describe.

One might want to use replaceFirst with all MineDown instances e.g. so that placeholders can work in gradients/rainbows.

Describe the solution you'd like

Either a per plugin setting or even a system property which toggles that.

Describe alternatives you've considered

Using a custom wrapper class or extending and overriding the replace method.

Additional context

#13