Rotate logs (#347)

* Reopen file/program outputs on SIGUSR1

When signaled with SIGUSR1, close and reopen file and program based
outputs. This is useful when combined with logrotate to rotate logs.

* Example logrotate config

Example logrotate config that relies on SIGUSR1 to rotate logs.

* Ensure options exist for all outputs

Options may not be provided for some outputs (like stdout), so create an
empty set of options in that case.

examples/logrotate/falco

@@ -0,0 +1,7 @@
+/var/log/falco-events.log {
+    rotate 5
+    size 1M
+    postrotate
+        /usr/bin/killall -USR1 falco
+    endscript
+}