API Design: define entities by archetype directly

[Avokadoen]

Building on the features made in the comptime branch we can design the API to utilize compile time more and enabling these features to be merged in master. Merging comptime branch in master will resolve issue #27

The user will have to define archetypes i.e:

const Player = struct {
   // Note variable name is not important here
   hp: Health,
   pos: Position,
   vel:  Velocity,
};

const StaticObject = {
   Pos: Position,
};

These archetypes are then stored in a comptime hash map

The API will not allow dynamically adding or removing components from an entity, but changing the entity type will be valid in any direction (or maybe this should be restricted?)

This will like mentioned allow the library to move a lot more over to compile time and hopefully make planned queries mostly compile time based as well and add the functionality for type queries i.e give me all Players

It will also make entity construction very fast since the user will always specify the full component list at creation i.e

world.setEntityType(entity, Player{...});

[Avokadoen]

each archetype should implement an interface
we can then have an array of these interfaces and then we can make some operations O(1) i.e hasComponent and getComponent etc...

The std.mem.Allocator is a good place to start for dynamic dispatch: https://github.com/ziglang/zig/blob/master/lib/std/mem/Allocator.zig

[Avokadoen]

The restriction of only allowing predefined archetypes can be removed by using the interface idea

Queries can be processed on compile time using comptime and itnerfaces can be used to do partial type erasure needed to combine different archetypes!

[Avokadoen]

Resolved by PR #30