Execute all the logic inside the after-build event
Execute all the logic inside the after-build event

This commit removes the need to use the before-build-all event for
initializing the state of the plugin. Instead, everything is initialized
in the after-build event, along with the minifying code.

This removes the chance of inconsistencies due to the global state used,
and possible errors if events are fired in the wrong order.

pietroalbini/lektor-minify,pietroalbini/lektor-minify,pietroalbini/lektor-minify,pietroalbini/lektor-minify