feat(order_utils.py): ERC20 asset data encoding and decoding

In addition to the ERC20 codec, also:

Stopped ignoring type errors on 3rd party imports, by including
interface stubs for them;
Removed the unimplemented signature-utils module, which was just a
stand-in when the python project support was first put in place.

https://github.com/0xProject/0x-monorepo/pull/1144

python-packages/order_utils/test/test_abi_utils.py

@@ -0,0 +1,53 @@
+"""Tests of 0x.abi_utils."""
+
+import pytest
+
+from zero_ex.dev_utils.abi_utils import (
+    elementary_name,
+    event_id,
+    method_id,
+    parse_signature,
+    simple_encode,
+)
+
+
+def test_parse_signature_type_error():
+    """Test that passing in wrong types raises TypeError."""
+    with pytest.raises(TypeError):
+        parse_signature(123)
+
+
+def test_parse_signature_bad_input():
+    """Test that passing a non-signature string raises a ValueError."""
+    with pytest.raises(ValueError):
+        parse_signature("a string that's not even close to a signature")
+
+
+def test_elementary_name_type_error():
+    """Test that passing in wrong types raises TypeError."""
+    with pytest.raises(TypeError):
+        elementary_name(123)
+
+
+def test_event_id_type_error():
+    """Test that passing in wrong types raises TypeError."""
+    with pytest.raises(TypeError):
+        event_id(123, [])
+
+    with pytest.raises(TypeError):
+        event_id("valid string", 123)
+
+
+def test_method_id_type_error():
+    """Test that passing in wrong types raises TypeError."""
+    with pytest.raises(TypeError):
+        method_id(123, [])
+
+    with pytest.raises(TypeError):
+        method_id("ERC20Token", 123)
+
+
+def test_simple_encode_type_error():
+    """Test that passing in wrong types raises TypeError."""
+    with pytest.raises(TypeError):
+        simple_encode(123)