add some aliases for submodules

.gitconfig

@@ -31,6 +31,9 @@
         getbranchcommitter = "!f() { git for-each-ref --format='%(committerdate) %09 %(committername) %09 %(refname)' | sort -k5n -k2M -k3n -k4n; }; f"
         grepp = grep --break --heading --line-number
         grephist = "!f() { regex=$1; git grep --break --heading --line-number -e $regex $(git rev-list --all); }; f"
+        sdiff = !"git diff && git submodule foreach 'git diff'"
+        spush = push --recurse-submodules=on-demand
+        supdate = submodule update --remote --merge
 [merge]
 	conflictstyle = diff3
 	tool = vimdiff