sha1dc: optionally use sha1collisiondetection as a submodule

diff --git a/RelNotes b/RelNotes
index 5fcc4ef74770e8587a1469fff5e3f5610dabf0e1..125bf78f3b9ed2f1444e1873ed02cce9f0f4c5b8 120000 (symlink)
--- a/RelNotes
+++ b/RelNotes
@@ -1 +1 @@
-Documentation/RelNotes/1.7.6.txt
\ No newline at end of file
+Documentation/RelNotes/2.13.0.txt
\ No newline at end of file