Restore deleted submodules

diff --git a/external/damsl-k3 b/external/damsl-k3
new file mode 160000 (submodule)
index 0000000..c7fe10b
--- /dev/null
+++ b/external/damsl-k3
@@ -0,0 +1 @@
+Subproject commit c7fe10bf2c1044f91426215d97f59a85d7c736c7

diff --git a/external/ekmett-parsers b/external/ekmett-parsers
new file mode 160000 (submodule)
index 0000000..eeb744b
--- /dev/null
+++ b/external/ekmett-parsers
@@ -0,0 +1 @@
+Subproject commit eeb744b5c7cae833b3142408751b33915b23429a

diff --git a/external/ekmett-trifecta b/external/ekmett-trifecta
new file mode 160000 (submodule)
index 0000000..3f4fbca
--- /dev/null
+++ b/external/ekmett-trifecta
@@ -0,0 +1 @@
+Subproject commit 3f4fbca985c01bb921d54a0874eefbe610a964ac