Dungeon cleanup

[surrsurus]

Dungeon needs more low-level, architectural work done. Related to #45 though not exactly.

• [x] Dungeon generation relies on a series of "filters" but they have a fairly loose definition. It would be constructive to further abstract these systems into Filter traits such that upon being given a list of such filters, an apply() or such can be ran to add the filter onto the dungeon map. This would solidify dungeon generation and make it slightly more comprehendible and gives a better interface for adding changes.
• [x] The structure system is ass and that whole file needs a ton of work to get it to an acceptable level.
• [x] I HATE having to do dungeon.grid it makes NO sense, what is the dungeon if the meaningful details are stored within the grid? I would love it if dungeon both had implementation and also was indexable. Maybe we can impl a trait for this? Basically I just want to hide Grid from anything that's not a Dungeon

[surrsurus]

Updated comment to have task manager. Also, added the Index and IndexMut trait to dungeons, as of 2f3d0e1. (About damn time!)

[surrsurus]

Filters also need some work, thought-wise at least. Filters need to have some type of grid obviously, some apply() function, and they all always must be indexable. It would be awesome to just have one struct that has all of that stuff enabled, since I really don't want to copy the index trait stuff around like 30 times.

[surrsurus]

So, the index trait thing is directly on Dungeon and Grid, haven't needed it on the Structure filter. I think all that needs to be done is to work on turning existing things into filters.