Bug 563994 – Input method module interface not documented

Bug 563994 – Input method module interface not documented

* gtk/gtkimcontext.h: Add public/private markers.
* gtk/gtkimcontext.c: Add section documentation which explains how
to add a new input method module to GTK+.  Document the signals and
virtual functions of GtkIMContextClass.
* gtk/gtkimmodule.c: Document struct GtkIMContextInfo.
* docs/reference/gtk/gtk-sections.txt: Add GtkIMContextClass and
GtkIMContextInfo to section GtkIMContext.
* docs/reference/gtk/Makefile.am (IGNORE_HFILES): Remove
gtkimmodule.h from the list in order to pick up GtkIMContextInfo.
* docs/reference/gtk/tmpl/gtkimcontext.sgml: Remove file from
repository since all the hand-edited content has been migrated to
source file comments.

svn path=/trunk/; revision=21870