tests/memfile: Test dump_meminit

Change tests/memfile to a mktest, moving the prior run-test.sh contents into a new read_dir.sh.
Add dump.ys (and friends) for testing dump_meminit.

tests/memfile/dump_gate.v

@@ -0,0 +1,19 @@
+module gate (
+    input clk, wen,
+    input [2:0] addr,
+    input [3:0] wdata,
+    output [3:0] rdata
+);
+
+reg [3:0] m [7:0];
+initial
+    $readmemh("gold.m.mem", m);
+
+always @(posedge clk) begin
+    if (wen)
+        m[addr] <= wdata;
+    else
+        rdata <= m[addr];
+end
+
+endmodule