; Improve doc strings in register.el

; Improve doc strings in register.el

* lisp/register.el (register-preview-delay)
(register-describe-oneline, register-preview-default)
(register-preview-function, register-preview, point-to-register)
(window-configuration-to-register)
(frame-configuration-to-register, jump-to-register)
(register-val-jump-to, number-to-register, increment-register)
(view-register, list-registers, register-val-describe)
(insert-register, register-val-insert, copy-to-register)
(append-to-register, prepend-to-register)
(copy-rectangle-to-register): Doc fixes.