Refactor tests (better grouping + cocotb support) (#15)

* initial refactor

* fix cocotb tests

* fix typecheck

* install verilator

tests/cocotb_lib/multiple_reg.rdl

@@ -0,0 +1,22 @@
+addrmap multi_reg {
+    reg {
+        field {
+            sw=rw;
+            hw=r;
+        } data[31:0];
+    } reg1 @ 0x0;
+
+    reg {
+        field {
+            sw=r;
+            hw=w;
+        } status[15:0];
+    } reg2 @ 0x4;
+
+    reg {
+        field {
+            sw=rw;
+            hw=r;
+        } control[7:0];
+    } reg3 @ 0x8;
+};