Example code in readme does not work with latest PyPI percol 0.2.1

[hartwork]

Hi!

I would like to vote for for a new release. The readme changes merged from 4b28037 are not supported: Once I fix the sting IO import for Python 3 (#107) I get ImportError: cannot import name 'no_output' from 'percol.actions' for a good reason: It does not exist in release 0.2.1. Can we have a new release please please?

If anyone needs a version of the example that works with Python 3.7:

from io import StringIO
from percol import Percol
from percol.actions import action

@action()
def no_output(lines, percol):
    "ignore all output"
    pass

def main(candidates):
    si, so, se = StringIO(), StringIO(), StringIO()
    with Percol(
            actions=[no_output],
            descriptors={'stdin': si, 'stdout': so, 'stderr': se},
            candidates=iter(candidates)) as p:
        p.loop()
    if p.args_for_action is None:
        raise KeyboardInterrupt
    results = p.model_candidate.get_selected_results_with_index()
    return [r[0] for r in results]

if __name__ == "__main__":
    candidates = ['foo', 'bar', 'baz']
    results = main(candidates)
    print("You picked: {!r}".format(results))

Best, Sebastian