how to resolve to a media processing function

[ichthyo]

We need a first draft/idea/design how to get at a raw processing function, which can be wired into a render node.

Things to consider

• usually we'll get this function from a "plugin"
• the access will be through an asset::Proc
• the plan is to use adapters or wrappers for the existing popular plugin systems
• on the usage site (within the low-level model), we just need
  • a function pointer
  • some one-size-fits-all convention how to feed the in/out buffer pointers to this function