Merge hooks into options and make each one an array option. This allows

multiple commands to be easily bound to one hook. set-hook and
show-hooks remain but they are now variants of set-option and
show-options. show-options now has a -H flag to show hooks (by default
they are not shown).

Makefile

@@ -56,7 +56,6 @@ SRCS=	alerts.c \
 	cmd-send-keys.c \
 	cmd-set-buffer.c \
 	cmd-set-environment.c \
-	cmd-set-hook.c \
 	cmd-set-option.c \
 	cmd-show-environment.c \
 	cmd-show-messages.c \
@@ -78,7 +77,6 @@ SRCS=	alerts.c \
 	format-draw.c \
 	grid-view.c \
 	grid.c \
-	hooks.c \
 	input-keys.c \
 	input.c \
 	job.c \