Do not rely on window reference count for linked formats because they
are also used for notifications, GitHub issue 4258.

Change pasting to bypass the output key processing entirely and write
what was originally received. Fixes problems with pasted text being
interpreted as extended keys reported by Mark Kelly.

Set visited flag on last windows when linking session.

Add detach-on-destroy previous and next, mostly from Alexis Hildebrandt.

Correct visited flag when the last window list is rebuilt by renumbering
windows, appears to fix hang reported by Mark Kelly.

Preserve marked pane when renumbering windows.

Do not attempt to update focus (and crash) when there is no previous window.

Add next_session_id format with the next session ID, GitHub issue 3078.

Do not destroy sessions twice, GitHub issue 2889.

Change focus to be driven by events rather than walking all panes at end
of event loop, this way the ordering of in and out can be enforced.
GitHub issue 2808.

Forbid empty session names, GitHub issue 2758.

Instead of forbidding invalid session names, sanitize them like window
names.

Add a number of new formats to inspect what sessions and clients a
window is present or active in. From Tyler Culp in GitHub issue 2034.

Merge hooks into options and make each one an array option. This allows
multiple commands to be easily bound to one hook. set-hook and
show-hooks remain but they are now variants of set-option and
sh

Merge hooks into options and make each one an array option. This allows
multiple commands to be easily bound to one hook. set-hook and
show-hooks remain but they are now variants of set-option and
show-options. show-options now has a -H flag to show hooks (by default
they are not shown).

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Break new window and pane creation common code from various commands and
window.c into a separate file spawn.c.

Tidy and rename some bits of status line code.

Support for windows larger than visible on the attached client. This has
been a limitation for a long time.

There are two new options, window-size and default-size, and a new
command, resize-window.

Support for windows larger than visible on the attached client. This has
been a limitation for a long time.

There are two new options, window-size and default-size, and a new
command, resize-window. The force-width and force-height options and the
session_width and session_height formats have been removed.

The new window-size option tells tmux how to work out the size of
windows: largest means it picks the size of the largest session,
smallest the smallest session (similar to the old behaviour) and manual
means that it does not automatically resize windows. The default is
currently largest but this may change. aggressive-resize modifies the
choice of session for largest and smallest as it did before.

If a window is in a session attached to a client that is too small, only
part of the window is shown. tmux attempts to keep the cursor visible,
so the part of the window displayed is changed as the cursor moves (with
a small delay, to try and avoid excess redrawing when applications
redraw status lines or similar that are not currently visible). The
offset of the visible portion of the window is shown in status-right.

Drawing windows which are larger than the client is not as efficient as
those which fit, particularly when the cursor moves, so it is
recommended to avoid using this on slow machines or networks (set
window-size to smallest or manual).

The resize-window command can be used to resize a window manually. If it
is used, the window-size option is automatically set to manual for the
window (undo this with "setw -u window-size"). resize-window works in a
similar way to resize-pane (-U -D -L -R -x -y flags) but also has -a and
-A flags. -a sets the window to the size of the smallest client (what it
would be if window-size was smallest) and -A the largest.

For the same behaviour as force-width or force-height, use resize-window
-x or -y, and "setw -u window-size" to revert to automatic sizing..

If the global window-size option is set to manual, the default-size
option is used for new windows. If -x or -y is used with new-session,
that sets the default-size option for the new session.

The maximum size of a window is 10000x10000. But expect applications to
complain and much higher memory use if making a window excessively
big. The minimum size is the size required for the current layout
including borders.

The refresh-client command can be used to pan around a window, -U -D -L
-R moves up, down, left or right and -c returns to automatic cursor
tracking. The position is reset when the current window is changed.

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SESSION_UNATTACHED flag is no longer necessary now we have an attached
count instead.

session_groups can be static also.

Improve logging of sessions.

Only show the first member of session groups in tree mode (-G flag
disables).

Some extra logging to show why tmux might exit.

Some new notifications, mainly for active pane and current window and
session:

pane-mode-changed
window-pane-changed
client-session-changed
session-window-changed

From Joshua Brot.

Log what is happening with window and session reference counts much more
obviously.

Do not update TERM into config file parsing has finished.