Extend the Archetype definition to give more possibilities in SIMD usage.

[Dandielo]

The idea is to add a 'width' information for each component type in an archetype. This width would define how many entities a single component is capable to contain.

Things that might need additional attention:

• Internal copy / move of component data when patching empty slots.
• Accessing sub-data from these components.

Quick prototype idea:
https://gist.github.com/Dandielo/ba8d9b020bbf40b8afef73ec63af8476