Add pipe element masking

[Wazzaps]

This means I can disable parts of the pipeline (from the end to the start) to debug each piece.
If I start with:
[ .[] | {(.ifname): .address} ] | add | .eth0
Then I should be able to switch to (with e.g shortcut: Shift+Left):
[ .[] | {(.ifname): .address} ] | add | .eth0
And then:
[ .[] | {(.ifname): .address} ] | add | .eth0
And then:
[ .[] | {(.ifname): .address} ] | add | .eth0