Refactoring, simplifying the interface between ring and vte-stream; required for
the forthcoming rewrapping feature. Paging is now a concept private to vte-stream.
Instead of telling when to turn page, the ring now advances the tail of the
streams, and vte-stream does paging on its own based on this information.

https://bugzilla.gnome.org/show_bug.cgi?id=336238#c74
Change suspicios code: resetting row_stream to 0 is fishy, I really do think
it needs to be set to ring->writable.

https://bugzilla.gnome.org/show_bug.cgi?id=336238#c75
Rewrap the lines when the window is resized.

https://bugzilla.gnome.org/show_bug.cgi?id=336238