More enums, fewer macros.

[unofficial-fish]

This is a constellation of related changes.

• Some macros are now enums.
• Some bitflag macros are also now enums. I've seen mixed thoughts on doing this, but the scratch-built parts of wipeout-rewrite use this idiom, so this makes it consistent.
• Removed some redundant parentheses. Enums do not have to worry about precedence.
• Removed an unused macro.
• Reorganized weapon.h since macros and enums mixed together looked strange.
• Changed section flags to bitshift notation.
• typedef particle_type_t - being as specific as possible with types seems like good practice to me. This could be applied to other enums.