sweeper: Add `post_step`, `post_predict`, and `post_sweep` hooks.

Signed-off-by: Matthew Emmett <memmett@gmail.com>
controllers: Call `post_*` hooks.

Signed-off-by: Matthew Emmett <memmett@gmail.com>
examples: Use hooks instead of chaining sweep/predict.

Signed-off-by: Matthew Emmett <memmett@gmail.com>
Merge pull request #107 from memmett/feature/post

Add `post_step`, `post_sweep`, and `post_predict` hooks.