Cleanup: move tag functions into own translation unit

Make dive.h a bit slimmer. It's only a drop in the bucket - but at
least when modifying tag functions not the *whole* application is
rebuilt anymore.

Signed-off-by: Berthold Stoeger <bstoeger@mail.tuwien.ac.at>

core/save-html.c

@@ -8,6 +8,7 @@
 #include "qthelper.h"
 #include "gettext.h"
 #include "divesite.h"
+#include "tag.h"
 #include <stdio.h>
 
 void write_attribute(struct membuffer *b, const char *att_name, const char *value, const char *separator)