New command to add md5 checksum machine tags

[samwilson]

As described in various places (e.g.) the easiest way to get a checksum of an uploaded file is to add your own md5 tag in the form checksum:md5=xxxxxx.

I propose a new command, checksums that takes a --hash parameter that specifies what hash function to use, and default to md5.

What do you think?

The idea is that then any uploading tool can check to see if a file has already been uploaded, and a duplicate-finding tool can find (exact) duplicates very easily.

[TheFox]

I would rather use sha1 as default instead. But this is a good idea.

[samwilson]

Yes, sha1 sounds good. Will do.

[samwilson]

Okay, I've started work on this in #34. I think it needs some work on the logging and usability perhaps.... let's discuss in that PR though. :-)