editor: move editor-related functions and declarations into common file
cache.h and strbuf.[ch] had editor-related functions. Move these into
editor.[ch].
Signed-off-by: Elijah Newren <newren@gmail.com>
Acked-by: Calvin Wan <calvinwan@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
authored by