Hash a File via CLI Tool

[joepetrowski]

As pointed out in the README, sometimes files are inputs to functions. However, sometimes (e.g. authorize_upgrade) a file's hash is needed. See e.g. this Stack Exchange question.

Feature Request: Add a CLI command to hash a file (presumably with Blake 256 as default).

[jacogr]

PRs welcome to add, should not be much work, but will take me ages to get to - so if urgent, PRs are welcome.