Add recording of evemu .events files

Introduce the concept of a "script format" to the preload, and support the
default (umockdev) and evemu's event formats.

Add -e/--evemu-events=devname=eventsfilename option to umockdev-record, to
record reads from an evdev device into an evemu .events file.

https://github.com/martinpitt/umockdev/issues/5