Lazy echo_via_pager

[macobo]

When outputting tens of thousands of lines of text via a pager, formatting it all at once might take a lot of time.

This cost can be hidden from the user by being lazy and only formatting the first few lines of output when the pager is called.The rest is generated on demand either as the user scrolls down or in a separate thread.

[fdavis]

Duplicate of #409
Closed by #889

Please reopen if this is a still an issue