This commit also consolidates the exit operations for consistency's
sake, and adds a kill() method to renderers for stopping them without
performing any final rendering.
v0.13.4 introduced a regression where lines weren't always cleared when
resizing the window resulting in the presence of rendering artifacts.
This commit fixes that.
The Nil Renderer essentially disables the Bubble Tea renderer sending
loggings and print statements to stdout. It can be enabled via the
ProgramOption WithoutRenderer.
Christian Muehlhaeuser
Christian Rocha