Restore padding

[nervo]

Introduce a new RestorePadding method, the exact opposite of ResetPadding, which set the padding at the same value it was juste before being resetted.

log.IncreasePadding()
log.IncreasePadding()
...

log.Info("some trivial info")

// Reset padding to highlight warning
log.ResetPadding()
log.Warn("be careful !!!")

// Restore padding to carry on as if nothing had happened
log.RestorePadding()

log.Info("some other trivial and boring info")

[caarlos0]

closing in favor of #5