patch 8.1.0825: code for autocommands is mixed with file I/O code

Problem:    Code for autocommands is mixed with file I/O code.
Solution:   Move autocommand code to a separate file. (Yegappan Lakshmanan,
            closes #3863)
diff --git a/src/proto.h b/src/proto.h
index cb4add0..e4153eb 100644
--- a/src/proto.h
+++ b/src/proto.h
@@ -62,6 +62,7 @@
 #  include "crypt.pro"
 #  include "crypt_zip.pro"
 # endif
+# include "autocmd.pro"
 # include "buffer.pro"
 # include "charset.pro"
 # ifdef FEAT_CSCOPE