Catmandu export support --id option to read identifiers from a file

[Patrick Hochstenbach]

 catmandu export MongoDB --bag pubs --id /tmp/ids.txt to YAML

[Nicolas Steenlant]

The id option already accepts an array of values, just make a space separated file and then call:

catmandu export MongoDB --bag pubs --id `cat /tmp/ids.txt` to YAML

If you need to export a really huge number of ids, we can add a new --id-file option?

[Nicolas Steenlant]

implemented in 4317ad3