ZFSBootMenu v1.0rc2

This release contains all of the fixes and features from 1.0rc1, as well as the following:

• Add support for reading the kernel commandline from the ZFS property org.zfsbootmenu:commandline. This property takes precedence over /etc/default/grub and /etc/default/zfsbootmenu
• Clean up or whitelist all issues in zfsbootmenu-lib.sh, zfsbootmenu-preview.sh and zfsbootmenu.sh noted by shellcheck.

A big thank you to @ahesford for his code contributions and testing leading up to this release candidate. It is very much appreciated!