Split frp part to standalone library

[xgrommx]

Hello @zyla

How about separate specular to specular-frp, specular-dom, specular-svg etc?

[zyla]

@xgrommx Hello, and sorry for the delay.

I was also thinking about that, especially since the -dom part has accumulated a lot of cruft, which could be two or three separate packages.

However, it's currently quite heavily coupled to the FRP part, and I have a rewrite of the FRP internals planned which will also require changes in the DOM part. However, once that stabilizes and the interface between the two is cleaned up, I will probably split into separate packages.