Shell tab completion for kat

[arrdem]

./kat should at least be able to tab-complete the available tasks

Relates to #2, in that server side tasks and script tasks both need to be enumerable depending on how the decomposition of task duties shakes out.

[arrdem]

Using list-tasks and jq -r .tasks[], it should be very simple to at least build up the list of supported tasks to tab complete against.

Flags for kat itself are hard-coded and unlikely to change.

Support for enumerating and tab completing targets is also possible via list-targets and jq -r '.targets|keys|.[]'