Pull common functionality out of treeburner into umbra

[simondevenish]

treeburner contains a large collection of utilities and objects that can support the development of any roguelike game. With some treatment of these treeburner classes, the capability of umbra could be expanded into a general rougelike engine/toolkit by refactoring these tools out of treeburner into umbra

[HexDecimal]

What I was doing was working on Umbra and it's sub-projects simultaneously, but this sounds like a better idea. The 3 projects using Umbra all share similar codebases, so it might work better to move the duplicate code to Umbra itself.

[simondevenish]

@HexDecimal I presume we want to refactor umbra code into namespaces as I have done on treeburner

[simondevenish]

That way treeburner code pulled into Umbra can be easily ported

[HexDecimal]

Yeah. Especially since this is supposed to be included into other projects. All these headers used to have an umbra_ prefix before, but I didn't add a namespace.

I'd probably go with umbra:: for everything. Maybe also umbra::widget::. Not sure about imod, that needs to be unabbreviated.