Use Travis CI to find syntax errors, undefined names

This repo is a _great_ resource.  Very helpful!!
* For Python 2.7, there are currently 3 syntax errors and 4 undefined names
* For Python 3.6, there are currently 17 syntax errors and 10 undefined names

This PR will add free automated flake8 testing of pull requests so you can find they easily.  The owner of the this repo would need to go to https://travis-ci.org/profile and flip the repository switch __on__ to enable free automated flake8 testing of each pull request.

.travis.yml

@@ -0,0 +1,26 @@
+language: python
+cache: pip
+python:
+    - 2.7
+    - 3.6
+    #- nightly
+    #- pypy
+    #- pypy3
+matrix:
+    allow_failures:
+        - python: nightly
+        - python: pypy
+        - python: pypy3
+install:
+    #- pip install -r requirements.txt
+    - pip install flake8  # pytest  # add another testing frameworks later
+before_script:
+    # stop the build if there are Python syntax errors or undefined names
+    - flake8 . --count --select=E901,E999,F821,F822,F823 --show-source --statistics
+    # exit-zero treats all errors as warnings.  The GitHub editor is 127 chars wide
+    - flake8 . --count --exit-zero --max-complexity=10 --max-line-length=127 --statistics
+script:
+    - true  # pytest --capture=sys  # add other tests here
+notifications:
+    on_success: change
+    on_failure: change  # `always` will be the setting once code changes slow down