Add replay hint to failure message

[brianrourkeboll]

Related to #696.

• Add a replay hint to the failure message when a test fails after more than 1 test. Enables easy copy-pasting for use like How to use last step's seed to reproduce the failing case #696 (comment).

The new hint is only shown if the test fails after more than 1 test; otherwise, the failure message remains the same.

I am open to wording or formatting suggestions if you think it could be improved.

Before

Falsifiable, after 2 tests (0 shrinks) (16007481833498190592,10453566836947007795).
Last step was invoked with size of 3 and seed of (10777961331788138723,17477835647268427641):

After

Falsifiable, after 2 tests (0 shrinks) (16007481833498190592,10453566836947007795).
Last step was invoked with size of 3 and seed of (10777961331788138723,17477835647268427641).
Replay directly at failing step with (10777961331788138723,17477835647268427641,3).

[kurtschelfthout]

looks great to me!