Improve command-line parsing and display.

- Allow the same form of specifying guest memory as in bhyveload and
  bhyve, with an optional [K|k|M|m|G|g|T|t] suffix.
- Change the program name and email address for bugs to be more
  bhyve/freebsd specific.
- Include the grub-bhyve version number in help display.
- Change the usage string and error handling to indicate that a VM
  name is a required parameter (bug report from Conrad Meyer).
Bump version to 0.30.