* Fix over-precise float formatting on Python 3
Sometimes tox would tell me things like
✔ OK py27 in 4.1370000000000005 seconds
✔ OK py36 in 14.5 seconds
✔ OK py37 in 15.029 seconds
✔ OK py35 in 17.519 seconds
✔ OK py34 in 18.85 seconds
the almost-rounded-to-3-decimals value was both funny and sad, but
mostly irritating.
This was happening because on Python 3 float.__str__ was changed to be
more precise, and now
>>> print(4 + 0.137)
4.1370000000000005
We can avoid the problem if we round the result of the addition instead
of adding a rounded number to the integer number of seconds:
>>> print(4.137)
4.137
I've also corrected the plural logic because "0.5 second" is wrong[*]:
https://ell.stackexchange.com/questions/7817/singular-or-plural-for-seconds
* Add myself to CONTRIBUTORS
Also sorted the CONTRIBUTORS file to make sure I've preserved the
alphabetical order, which adjusted some existing names.
* Add a news fragment
* Make the linter happy