implicit address-taking for array slices

TODO.md

@@ -144,6 +144,13 @@
 9. allow pointer field access pass-through (implemented)
   - having a pointer (`ptr`) to a struct, we should allow access through `ptr.field` as opposed to mandating `ptr^.field`
 
+10. make slice expressions on array variables implicitly address-taking (implemented)
+  - zig's slice expression on an array variable handles the address-taking implicitly (nice ergonomics)
+  - `arr[a..b]` on an array variable now slices without the explicit `&`; the
+    explicit `(&arr)[a..b]` pointer-to-array form keeps working unchanged
+  - array rvalues (e.g. a by-value array return) are materialized into a
+    temporary before slicing, matching the for-loop iterable lowering
+
 ## A word on multi-unwrap
 
 Unwrap multiple optionals with `and`. This **short-circuits**: if the first optional is none, subsequent expressions are not evaluated.