v2.1.0 release

Change log:
//add add.if.* sub-command
kiss-vm: add sub-command add.if.bridge
kiss-vm: add sub-command add.if.passthr
//support multi-arch Guest on amd64 host
kiss-vm: add option --arch to support multi-arch
kiss-vm: add option --qemucpu
utils: add qemu-system-archs-install.sh

Full Changelog: v2.0.4...v2.1.0