Documentation: Added the USE_PLAYER_ENERGY flag from existing code

[RedMisao]

Summary

Infrastructure "Documentation: Added the USE_PLAYER_ENERGY flag from existing code"

Purpose of change

Added the USE_PLAYER_ENERGY flag in the JSON_FLAGS.md doc and a brief description of what it does. The actual code was added some time ago by KorG I believe, but the documentation was missing.
Also minor editions to the doc itself: moved Use actions from Books into Tools, added format to the FILTHY flags, and added the Effects title linking in the index.

Describe the solution

Describe alternatives you've considered

Testing

1. Created a new PC with a modded item that casts spells using the USE_PLAYER_ENERGY flag.
2. Checked mana pool: 1000 units.
3. activated the item, casted a spell that costs 200 units.
4. Spell was casted, mana pool was reduced by 200 units.

Additional context

These images show that the flag is working as intended for the last August 15 experimental.

(Note: this to show the total mana pool, I don't know how to enable displaying the mana pool on the sidebar)

I feel like the line count is weird

[Maleclypse]

Do you need to rebase? I'm trying to understand why your 1 line change is changing 100 lines?

[RedMisao]

Do you need to rebase? I'm trying to understand why your 1 line change is changing 100 lines?

I also moved the "Use actions" section that was under "Books" to the "Tools" section.