Adding a content size meta?

[Julien Blanchard]

Thanks to gemini://konpeito.media I noticed we might be missing the
content size information in some cases, mostly binary files.
With content that takes some time to be downloaded it would be nice to
be able to show the user the download progress. Most clients currently
leave the user in the dark regarding what's happening. Since I hope
that Gemini will be used for more medium than text as cat uses it,
this would be a nice addition to clients.
I would imagine this added meta only for non `text/whatever` content.

There is also another need I felt being a client developer, it's
knowing what mime type an URL will return to be able to treat/display
it differently without necessarily getting the content.  Could we
imagine a standardized way to query an URL just for it's meta header
maybe?

These are really client dev concerns and I feel this might be overkill
and going against the simplicity we want but I had to ask :)