Support for running gganimate::animate() in parallel

[HenrikBengtsson]

Proof-of-concept support for running gganimate::animate() in parallel, cf. Issue #78.

Progress reporting can be handled too but that requires discussions.

## Adopted from example("animate", package = "gganimate")

library(gganimate)

anim <- ggplot(mtcars, aes(mpg, disp)) +
  transition_states(gear, transition_length = 2, state_length = 1) +
  enter_fade() +
  exit_fade()

future::plan("sequential")  ## default
t0 <- system.time(animate(anim))
print(t0)

future::plan("multiprocess", workers = 4L)
t1 <- system.time(animate(anim))
print(t1)

print(t0 / t1)
##      user    system   elapsed 
## 2.2802385 0.9121339 2.5819751

[phileas-condemine]

@thomasp85 is this going to be merged ?

[rrmn]

@thomasp85 This is an awesome PR imo. What do you think about it?

[jzadra]

Is this still planned? It would be a great feature!

[chicodias]

this is FUTURE!!