* rst.el: Revamp section title faces.

* rst.el: Revamp section title faces.
(rst-official-version)
(rst-package-emacs-version-alist): Sync with official version
V1.4.0.
(rst-faces-defaults, rst-set-level-default)
(rst-level-face-max, rst-level-face-base-color)
(rst-level-face-base-light, rst-level-face-format-light)
(rst-level-face-step-light, rst-define-level-faces): Obsolete.
(rst-adornment-faces-alist): Match new setup.
(rst-level-1, rst-level-2, rst-level-3, rst-level-4)
(rst-level-5, rst-level-6): New faces.