grapes-less-than-less-than-grapes: Append to a list or environment, overwriting if necessary.
In syberia/director: Load, track, and manage dependencies in a file structure.

Append to a list or environment, overwriting if necessary.

1	obj1 %<<% obj2

`obj1.`	The object to be appended to.
`obj2.`	The object to append.

## Not run: 
  x <- list(a = 1)
  x %<<% list(b = 2) # list(a = 1, b = 2)
  x %<<% list(a = 2) # list(a = 2)
  y <- list2env(x)
  y %<<% list(b = 2) # environment with a = 1 and b = 2
  y %<<% list2env(list(b = 2)) # same as above
  y %<<% list(a = 2) # environment with a = 2

## End(Not run)