compat: provide Memory shim.

doc/COMPAT_SUMMARY.md

@@ -54,11 +54,11 @@ Compatibility summary
       - (−) `Tristate` ?
       - (+) `TSTriple` → `.lib.io.TSTriple`, `bits_sign=`→`shape=`
       - (−) `Instance` ?
-      - (−) `Memory` id
-        - (−) `.get_port` **obs** → `.read_port()` + `.write_port()`
-      - (−) `_MemoryPort` **obs**
+      - (+) `Memory` id
+        - (+) `.get_port` **obs** → `.read_port()` + `.write_port()`
+      - (+) `_MemoryPort` **obs**
         <br>Note: nMigen separates read and write ports.
-      - (−) `READ_FIRST`/`WRITE_FIRST` **obs**
+      - (+) `READ_FIRST`/`WRITE_FIRST` **obs**
         <br>Note: `READ_FIRST` corresponds to `mem.read_port(transparent=False)`, and `WRITE_FIRST` to `mem.read_port(transparent=True)`.
       - (-) `NO_CHANGE` **brk**
         <br>Note: in designs using `NO_CHANGE`, repalce it with an asynchronous read port and logic implementing required semantics explicitly.