Merge remote-tracking branch 'origin/merge-requests/256'

After more than ten years, archiso is once again using GRUB. GRUB! Only this time, it's for UEFI not BIOS boot.

By plainlinen
* origin/merge-requests/256:
  Update documentation for uefi x64 grub boot modes
  Use grub for uefi x64 boot modes in profiledef.sh
  Add *_uefi-x64.grub.* functions to mkarchiso
  Add useful grub menu entries to grub.cfg

Closes #63 and #159

See merge request !256.