#210 Add converters %S and %T to utils.str.format

[Valentin Lorentz]

Hi,

%S displays a file size in a human-readable way (and potentially localizable): https://github.com/ProgVal/Limnoria/commit/e556fbde2e1f888ce79b19de30ae7e788ab7d75a

%T displays a time delta (as used in Later):
https://github.com/ProgVal/Limnoria/commit/8b4b45ecf067af5f0049972b193b28accf5e1a2e
https://github.com/ProgVal/Limnoria/commit/1e050d7fa82e869e084b0369dde5ce8aa38c143a
https://github.com/ProgVal/Limnoria/commit/4e9bb2c24168ef9b0af1d4c7ef8db242585fa43c

Regards,
Valentin