[elementary] Documenting/exemplifying the following:

[elementary] Documenting/exemplifying the following:
 - elm_gengrid_item_append
 - elm_gengrid_item_prepend
 - elm_gengrid_item_bring_in
 - elm_gengrid_item_show
 - elm_gengrid_item_insert_after
 - elm_gengrid_item_insert_before
 - elm_gengrid_item_size_get
 - elm_gengrid_item_size_set
 - elm_gengrid_selected_item_get
 - elm_gengrid_selected_items_get
 - elm_gengrid_first_item_get
 - elm_gengrid_last_item_get

git-svn-id: svn+ssh://svn.enlightenment.org/var/svn/e/trunk/elementary@61705 7cbeb6ba-43b4-40fd-8cce-4c39aea84d33