SPIRE: add support for [automatically] rotating log files

[sorindumitru]

It would be good if SPIRE got some support for automatically rotating log files. This can be currently done through a signal on systems that support it, but it won't work on Windows. It would be good if SPIRE would either:

• Get support for automatically rolling files, maybe through something like lumberjack
• Add some other way to trigger re-opening the file, maybe in the Logger API.

[MarcosDY]

May we support events instead?