Added documentation to the nuget package

API changes:

• Added LumpType enum
• Methods that previously accepted an int lump index now accepts a LumpType instead
• GameLumpItem is now immutable
• GameLump and GameLumpItem has been rewritten. The ability to add/remove GameLumpItems to the GameLump now works correctly
• Removed the dataWritten parameter to PakfileLump.CloseArchiveStream
• Removed BSP zero padding at the end