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

* initial refactor

* fix cocotb tests

* fix typecheck

* install verilator

tests/cocotb_lib/simple.rdl

@@ -0,0 +1,8 @@
+addrmap simple_test {
+    reg {
+        field {
+            sw=rw;
+            hw=r;
+        } data[31:0];
+    } test_reg @ 0x0;
+};