Adding engine.js file

[HolyRomanEmperor]

refactored code - added engine.js file, which contains logic common to AoE2 and RoR, similar to main.js

added more charge types

[HSZemi]

To be honest, I'd rather leave the RoR tech tree alone until we are able to automatically layout individual civ tech trees.

I did however incorporate the class description updates in d17d049 and the additional charge types in 4fcf376, thank you for that 💛

[HolyRomanEmperor]

Can you also pull in the following changes:

• main.js: if ([6, 7].includes(meta.ChargeType) && meta.ChargeEvent) {
  stats.push('Charge Attack Range: ' + (meta.ChargeEvent + meta.Range));
  }
• All changes in scripts/README.md
• All changes in scripts/generateBuildingTechUnitImages.py
• All except specific to RoR in scripts/generateDataFiles.py