Merge MV and MZ versions to one single base

[00due]

Is your feature request related to a problem? Please describe.
This would ease the maintaining and pull requests with contributions to just one version by a lot.

Describe the solution you'd like
Check if the game uses MV or MZ, and make engine-specific calls check the engine version.

Describe alternatives you've considered

Additional context
Will be worked on when I have time and I'm up to it.

[TheRealFame]

Don't forget to declare that this plugin also works for mv!

[00due]

Won't forget, but this plugin has been unmaintained for 10 months, and I have no real need to complete this request.

If there will be another update in the future, then I will look into it.