Allows for custom weather types.
In SOC:
```Freeslot
PRECIP_GROOVY
Weather PRECIP_GROOVY
Type = MT_PARTICLE
Effects = PRECIPFX_THUNDER|PRECIPFX_LIGHTNING```
In Lua:
```freeslot("PRECIP_GROOVY")
precipprops[PRECIP_GROOVY] = {
type = MT_PARTICLE,
effects = PRECIPFX_THUNDER|PRECIPFX_LIGHTNING
}```
Then in level header, simply set `Weather = PRECIP_GROOVY`.
Other properties are part of the object itself:
- Falling speed is set as the object's speed
- Sound ID is set via the object's SeeSound
- Sound frequency is set by the object's Mass.
* Rework HU_UpdatePatch to HU_UpdateOrBlankPatch with a "required" boolean.
* If desired graphic is not present in resources:
* If required is true, return `missingpat`.
* If false, return NULL as before (font compatibility).
* Add an alias with the previous function signature, so you don't need to add a million `true`s everywhere.
* Remove a ton of irrelevant graphics the game attempts to cache only because of code inherited from vanilla SRB2.
* Remove the unused hudinfo system, also inherited from vanilla SRB2.
