Merge pull request #1826 from quantopian/add-engine-docs

Add engine docs

tests/pipeline/test_filter.py

@@ -49,8 +49,8 @@ def rowwise_rank(array, mask=None):
     Take a 2D array and return the 0-indexed sorted position of each element in
     the array for each row.
 
-    Example
-    -------
+    Examples
+    --------
     In [5]: data
     Out[5]:
     array([[-0.141, -1.103, -1.0171,  0.7812,  0.07  ],

tests/pipeline/test_term.py

@@ -147,8 +147,8 @@ def to_dict(l):
     """
     Convert a list to a dict with keys drawn from '0', '1', '2', ...
 
-    Example
-    -------
+    Examples
+    --------
     >>> to_dict([2, 3, 4])  # doctest: +SKIP
     {'0': 2, '1': 3, '2': 4}
     """