Comrade extension

[ptiede]

I think we may want to move most of the Comrade extension stuff to Comrade proper. The biggest reason right now is that the current Comrade extension does type piracy on extract_table, imo, since Comrade owns that method and the generic dispatch of AbstractVector could lead to issues.

The other reason is that I also need to add support for closures, which the Comrade VLBIData extension already does, but I'd prefer if all the table extraction stuff lived in the same repo.

[aplavin]

Makes sense! If tests pass (https://github.com/JuliaAPlavin/VLBIData.jl/blob/master/test/comrade.jl) would be happy to drop the extension here. It was only added because it was the fastest way for me not to use pyehtim a few months ago :)
Comrade's data structures are definitely more involved than flat uvtable here, so even conceptually it seems best to have the extension there.