Add window-tree based, atomic and side window functions to window.el.

Add window-tree based, atomic and side window functions to window.el.

* window.el (window-right, window-left, window-child)
(window-child-count, window-last-child, window-any-p)
(normalize-live-buffer, normalize-live-frame)
(normalize-any-window, normalize-live-window)
(window-iso-combination-p, window-iso-combined-p)
(window-iso-combinations)
(walk-window-tree-1, walk-window-tree, walk-window-subtree)
(windows-with-parameter, window-with-parameter)
(window-atom-root, make-window-atom, window-atom-check-1)
(window-atom-check, window-side-check, window-check): New
functions.
(ignore-window-parameters, window-sides, window-sides-vertical)
(window-sides-slots): New variables.
(window-size-fixed): Move down in code.  Minor doc-string fix.