Add rename/mv command. This is the logical equivalent of copy and remove, and is in fact implemented as such. It doesn't use the remove command directly.

diff -r 3903775176ed b
--- /dev/null
+++ b/b
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+123
diff -r 3903775176ed b
--- /dev/null
+++ b/b
@@ -0,0 +1,1 @@
+123