Revert "Add -I / --online-input for huge top-level arrays"

This reverts commit 77936a594d797c480f26bfcef3636a74588a6918.

That commit was a mistake.  It had a number of bugs, to start, but also
it's the wrong design.

For online input handling what we should want is for the parser to emit
arrays of index and value (when exploding just the top-level) or path
and value (when exploding further).  The type of index should indicate
whether a) the container is an array (index is number), b) the container
is an object (the index is a string), or c) there is no container
(top-level is not an array or object).

Conflicts:

	main.c
Add `yield`
Test yield
Document yield
Explain `empty` more
Explain `reduce` more