Add memory debug and profile (#130)

* Add code for memory consumption and optionally select which debug you would like to use.

* Add documentation about debuging

* Add psutil

* Tests updates

* Fix lint

* Add extra tests

* Update MLPrimitives version

* Rephrase documentation

Author: pvk-developer

docs/advanced_usage/pipelines.rst

@@ -423,6 +423,42 @@ An example of this situation, where we want to reuse the output of the first blo
     predictions = pipeline.predict(X_test)
     score = compute_score(y_test, predictions)
 
+Pipeline debugging
+------------------
+
+Sometimes we might be interested in debugging a pipeline execution and obtain information
+about the time, the memory usage, the inputs and outputs that each step takes. This is possible
+by using the argument ``debug`` with the method ``fit`` and ``predict``. This argument allows us
+to retrieve critical information from the pipeline execution:
+
+* ``Time``: Elapsed time for the primitive and the given stage (fit or predict).
+* ``Memory``: Amount of memory increase or decrease for the given primitive for that pipeline.
+* ``Input``: The input values that the primitive takes for that specific step.
+* ``Output``: The output produced by the primitive.
+
+
+If the ``debug`` argument is set to ``True`` then a dictionary will be returned containing all the
+elements listed previously::
+
+    result, debug_info = pipeline.fit(X_train, y_train, debug=True)
+
+In case you want to retrieve only some of the elements listed above and skip the rest, you can
+pass an ``str`` to the ``debug`` argument with any combination of the following characters:
+
+* ``i``: To include inputs.
+* ``o``: To include outputs.
+* ``m``: To include used memory.
+* ``t``: To include elapsed time.
+
+For example, if we are only interested on capturing the elapsed time and used memory during the
+``fit`` process, we can call the method as follows::
+
+    result, debug_info = pipeline.fit(X_train, y_train, debug='tm')
+
+.. warning:: Bear in mind that if we use ``debug=True`` or saving the ``Input`` and ``Output``,
+             this will consume extra memory ram as it will create copies of the input data and
+             the output data for each primitive. For profiling it is recommended using the option
+             ``tm`` as shown in the previous example.
 
 .. _API Reference: ../api_reference.html
 .. _primitives: ../primitives.html