Run a proc stored in an object in another thread with a threadpool

[mratsim]

I have no doc in weave-io because I didn't change the internals to optimize for 
IO 😅

Do you have code? You say nimcall but it;s
    
    
    type Actor = ref object
      field1: int
      field2: int
      command: proc(x,y: int)
    
    
    Run

instead of
    
    
    type Actor = ref object
      field1: int
      field2: int
      command: proc(x,y: int) {.nimcall.}
    
    
    Run