Wishlist metadata improvements: arbitrary keys, non-argument input

[chrishiestand]

It would be really helpful to be allowed to set arbitrary keys in the metadata. Currently the only keys supported are author, keywords, subject, title.

Accepting metadata from the command line is problematic because metadata can contain quotes or other shell character which make batch processing a little complicated - at least shell escapes are required.

So it would also be great if there was a way to, e.g., read metadata from a file or stdin instead of a command line. The file could simply be a json dictionary of key/value pairs - json is very friendly to modern day development :-)

A tool that can do this well is currently missing in the PDF market - no tool does this well (not pdftk, Zend, pypdf, etc...)