ZFSBootMenu 0.7.3

This release adds the helper bin/generate-zbm which can help control the lifecycle of a the components needed to boot a system. It can generate a versioned kernel and initramfs, and/or a combined kernel/initramfs/commandline EFI executable. The helper script is able to able to do un-versioned files as well, creating initramfs-zfsbootmenu.img and then rotating that into initramfs-zfsbootmenu-backup.img when a new initramfs is created.

To better integrate with boot loaders like rEFInd, the option 'timeout' can be set on the command line when booting into the bootmenu.

A value of 0 will bypass the countdown timer and menu screens, attempting to boot the environment set by bootfs.
A value of -1 will force you into the menu system, where you can pick a boot environment, kernel, snapshot etc.
Any positive integer value will enable the countdown timer, where the system will then attempt to boot the environment set by bootfs.

The default timeout value remains at 10 seconds, consistent with previous behavior.