Allow Character Layering

[Enthalpy]

It is proposed that a system be added to let characters layer. Right now, the order in which characters "stack" on top of each other is determined by the order in which they were added. This proposal would abstract the two apart, so the user can directly determine the stacking order.

[Enthalpy]

As a further complication, it is currently impossible to commute the layer of two characters on the same place. Any attempt to do this needs ugly workarounds, like two places that look the exact same.