Rewrite buffer display related doc-strings and doc

Rewrite buffer display related doc-strings and doc

* lisp/window.el (display-buffer-overriding-action)
(display-buffer-alist, display-buffer-base-action)
(display-buffer-fallback-action, display-buffer-assq-regexp)
(display-buffer): Rewrite doc-strings using suggestions by
Alan Mackenzie <acm@muc.de>.
(display-buffer-use-some-frame): Adjust doc-string and
reformat code.
* doc/lispref/windows.texi (Buffer Display Action Alists):
Make docs on 'window-height', 'window-width' and
'preserve-size' entries more accurate.