Update Level.cs

Added support for the last few missing settings in Anvil worlds. This includes:
- generatorVersion
- generatorOptions
- initialized
- allowCommands
- DayTime
- GameRules:
  - commandBlockOutput
  - doFireTick
  - doMobLoot
  - doMobSpawning
  - doTileDrops
  - keepInventory
  - mobGriefing
Update Level.cs

Removed SchemaOptions.OPTIONAL from all sub nodes of GameRules. As far as I can see GameRules is mandatory
Merge pull request #13 from snoopen/patch-1

Update Level.cs