Fix a lot of old docs code that doesn't exist anymore

jedi/_compatibility.py

@@ -268,7 +268,7 @@ def use_metaclass(meta, *bases):
     """ Create a class with a metaclass. """
     if not bases:
         bases = (object,)
-    return meta("HackClass", bases, {})
+    return meta("Py2CompatibilityMetaClass", bases, {})
 
 
 try:

jedi/evaluate/__init__.py

@@ -17,7 +17,8 @@ said, the typical entry point for static analysis is calling
 ``eval_expr_stmt``. There's separate logic for autocompletion in the API, the
 evaluator is all about evaluating an expression.
 
-TODO this paragraph is not what jedi does anymore.
+TODO this paragraph is not what jedi does anymore, it's similar, but not the
+same.
 
 Now you need to understand what follows after ``eval_expr_stmt``. Let's
 make an example::

jedi/evaluate/base_context.py

@@ -1,3 +1,11 @@
+"""
+Contexts are the "values" that Python would return. However Contexts are at the
+same time also the "contexts" that a user is currently sitting in.
+
+A ContextSet is typically used to specify the return of a function or any other
+static analysis operation. In jedi there are always multiple returns and not
+just one.
+"""
 from parso.python.tree import ExprStmt, CompFor
 
 from jedi import debug