Thunder shield-related changes

See merge request KartKrew/Kart-Public!110

Kill invincibility item caps

See merge request KartKrew/Kart-Public!108

This reverts commit 8780800e.

It's a holdover from another era, our item changes have stacked up enough that we don't really need this cap anymore

16 more colors

See merge request KartKrew/Kart-Public!101

Assorted item tweaks

See merge request KartKrew/Kart-Public!85

Use long double suffix

See merge request KartKrew/Kart-Public!98

Fix SIGSEGV from sending lindefs/sidedefs in savegame

See merge request KartKrew/Kart-Public!99

On second thought, the old method is "sneakier"

- Increase gravity of super-forward throws
- Revert explosion radius change
- Nerf generic explosion stun (SPB explosion stun is identical)

- SPB Rush odds are not affected by player count.
- Thunder Shield cannot be rolled with SPB out.
- Reticule is displayed on minimap while SPB is out.

- Start cooldown deactivates exactly 30 sec, instead of after 30 seconds. Barely affects gameplay but it looks slightly less of a magic number looking at the code.
- Prevent multiple Thunder Shields being out via normal means.
- Slightly loosened up the invincibility item limits -- gives more invincibility items sooner for odd player counts but doesn't affect the numbers for the game's balancing points (4P, 8P)
- Update comments