Allow using our own rake tasks

[phillipoertel]

rspec-rerun is just what we need, but we have our own rake tasks (using parallel_test, for example, or only a subset of all spec files), which we would like to run with rspec-rerun.

[dblock]

Check out the implementation in rspec.rake. I wonder whether this gem can actually do a smart substitution to accomodate truly custom runs. Feel free to suggest something workable.

[sgringwe]

I would also appreciate this ability. I use knapsack on circleci.