(Hooks): Delete confusing and unnecessary sentence.

(Hooks): Delete confusing and unnecessary sentence.
(Major Mode Conventions): Refer to `Auto Major Mode' in more
appropriate place.
(Derived Modes): Small clarifications.
(Minor Mode Conventions, Keymaps and Minor Modes): Replace
references to nodes with references to anchors.
(Mode Line Data): Warn that `(:eval FORM)' should not load any files.
Clarify description of lists whose first element is an integer.
(Mode Line Variables): Add anchor.
(%-Constructs): Clarify description of integer after %.
(Emulating Mode Line): Describe nil value for FACE.