This can be set to 'none' (the default), 'osd', 'log' or 'both'.
When 'osd' is enabled, we'll render the frame rendering time to a
sub-surface after each frame.
When 'log' is enabled, the frame rendering time is logged on stderr.
The default is still to inverse the regular foreground/background
colors.
If the user sets *both* of the new options, selection-foreground and
selection-background, those colors will *always* be used for selected
cells, instead of inverting the regular foreground/background colors.
When enabled, the mouse cursor is hidden when the user types in the
terminal. It is un-hidden when the user moves the mouse, or when the
window loses keyboard focus.
* Move 'scrollback' to 'scrollback.lines'
* Move (the new) 'scrollback-indicator-*' options to
'scrollback.indicator-*'
Log a deprecation warning when the old 'scrollback' option is used,
but don't remove it, yet.
