Revert "Migrate as much as possible to pip and requirements.txt"

This reverts commit 982594a4a5.

lib/html5lib/trie/__init__.py

@@ -0,0 +1,12 @@
+from __future__ import absolute_import, division, unicode_literals
+
+from .py import Trie as PyTrie
+
+Trie = PyTrie
+
+try:
+    from .datrie import Trie as DATrie
+except ImportError:
+    pass
+else:
+    Trie = DATrie