Allow dynamic generation of the autocompletion list using a callback.
Allow dynamic generation of the autocompletion list using a callback.

The callback receives the following data:
 - The current click context. This allows the callback to access any
   parameters that are already present on the command line.
 - The current word being completed. This may be an empty string.
 - The bash COMP_CWORDS and COMP_CWORD variables, in case the callback
   wants to do raw parsing of this data.

Nudies/click,pallets/click,mitsuhiko/click