Adding scaling & reference

Quick update here after some feedback. 

• Added usage number scaling to "Oath of Protection"
• Change disadvantage in "Oath of Protection" to reducing damage (scaling with level, starting flat 2)
• Added a reference page to the random magic shield table in the core book (page 284)
• Clarified "Defensive Fighting Style" usage to also apply to the guarded target
• Clearer wording on "Defensive Fighting Style" to be closer to the "sunder" rule from Cursed Scroll 3

Concerning some feedback on

•  AC scaling  - the talent mirrors the fighter talent in their tree and is even weaker. 
  • No changes were made
• Charging with horses and advantage. That is a DM ruling, it only applies to outside scenarios and does not factor into dungeon crawling. I deem it a unique feature, enough to keep it. Thus: 
  • No changes were made

Thanks to everyone on the Shadowdark Discord in the post and on the Dolmenwood Conversion Thread. Your feedback was invaluable.