diskimg: write disk images

Usage:
	diskimg [-a algo] [-v] image device

Flags:
	-a algo		Select the hashing algorithm to use. The default
			is 'sha256'. Specifying an algorithm of 'list'
			will print the supported algorithms to standard
			output and exit with error code 2.
	-v		Enable verbose (debug) output.

Examples:
	
	Copying images/server.img to /dev/sda:

	$ sudo diskimg images/server.img /dev/sda

	Write a bladerunner node image to /dev/sda:

	$ sudo diskimg -v ~/code/bladerunner/packer/build/cm4-cnode-ubuntu-22.04.2.img /dev/sda
	opening image /home/kyle/code/bladerunner/packer/build/cm4-cnode-ubuntu-22.04.2.img for read
	/home/kyle/code/bladerunner/packer/build/cm4-cnode-ubuntu-22.04.2.img  416d4c8f890904167419e3d488d097e9c847273376b650546fdb1f6f9809c184
	opening device /dev/sda for rw
	writing /home/kyle/code/bladerunner/packer/build/cm4-cnode-ubuntu-22.04.2.img -> /dev/sda
	wrote 4151312384 bytes to /dev/sda
	syncing /dev/sda
	verifying the image was written successfully
	OK

Motivation:

	I wanted to write something like balena's Etcher, but commandline only.