ACER algorithm (#184)

* initial ACER commit

* Code cleanup + several fixes

* Q-retrace bug fix + small clean-ups

* added documentation for acer

* ACER benchmarks

* update benchmarks table

* Add nightly running of golden and trace tests. (#202)

Resolves #200

* comment out nightly trace tests until values reset.

* remove redundant observe ignore (#168)

* ensure nightly test env containers exist. (#205)

Also bump integration test timeout

* wxPython removal (#207)

Replacing wxPython with Python's Tkinter.
Also removing the option to choose multiple files as it is unused and causes errors, and fixing the load file/directory spinner.

* Create CONTRIBUTING.md (#210)

* Create CONTRIBUTING.md.  Resolves #188

* run nightly golden tests sequentially. (#217)

Should reduce resource requirements and potential CPU contention but increases
overall execution time.

* tests: added new setup configuration + test args (#211)

- added utils for future tests and conftest
- added test args

* new docs build

* golden test update

docs/selecting_an_algorithm.html

@@ -364,6 +364,14 @@ $(document).ready(function() {
             learning stability and speed, both for discrete and continuous action spaces.
          </span>
       </div>
+      <div class="algorithm discrete on-policy requires-multi-worker" data-year="201707">
+         <span class="badge">
+            <a href="components/agents/policy_optimization/acer.html">ACER</a>
+            <br>
+            Similar to A3C with the addition of experience replay and off-policy training. to reduce variance and
+            improve stability it also employs bias correction and trust region optimization techniques.
+         </span>
+      </div>
       <div class="algorithm continuous off-policy" data-year="201509">
          <span class="badge">
             <a href="components/agents/policy_optimization/ddpg.html">DDPG</a>
@@ -480,7 +488,8 @@ algorithms for imitation learning in Coach.</p>
         <script type="text/javascript" src="_static/jquery.js"></script>
         <script type="text/javascript" src="_static/underscore.js"></script>
         <script type="text/javascript" src="_static/doctools.js"></script>
-        <script async="async" type="text/javascript" src="https://cdnjs.cloudflare.com/ajax/libs/mathjax/2.7.1/MathJax.js?config=TeX-AMS-MML_HTMLorMML"></script>
+        <script type="text/javascript" src="_static/language_data.js"></script>
+        <script async="async" type="text/javascript" src="https://cdnjs.cloudflare.com/ajax/libs/mathjax/2.7.5/latest.js?config=TeX-AMS-MML_HTMLorMML"></script>