v0.7.2

engine: exit on Ctrl-D, just like Ctrl-C

Many common CLI applications quit when stdin reaches end-of-file, as
triggered by Ctrl-D. (Examples: `python`, `bash`, `node`, `gdb`, `ed`.)
Though `jiq` is more of a TUI than a CLI, exiting with Ctrl-D still
feels familiar and intuitive to me, and was how I tried to exit `jiq`
the first time that I used it.

wchargin-branch: ctrl-d-exit
wchargin-source: b3ac9be9ce4378b8c3eb82e6d3bc3bb6403d3309