[feature request] ability to **add** custom global variables

[ClosedPort22]

It would be nice to be able to add custom global variables instead of replacing util.GLOBALS. Currently I use a separate configuration profile for a postprocessor that needs some custom logic, but this workaround falls short when I need to use built-in functions in the same postprocessor.

[mikf]

Add these lines to your module:

from gallery_dl import util
globals().update(util.GLOBALS)

[mikf]

I did update globals such that it updates the GLOBALS dict instead of overwriting it (a1ca240).

[ClosedPort22]

Thank you!