Use Travis Continuous Integration to run flake8 on all code changes

https://github.com/marketplace/category/continuous-integration

To start the automated testing of all pull requests, log into https://travis-ci.com/TheYahya using GitHub credentials and turn the repo switch ___on___.

Other tests can be added to the __script:__ section.

.travis.yml

@@ -0,0 +1,25 @@
+group: travis_latest
+language: python
+cache: pip
+matrix:
+  allow_failures:
+    - python: nightly
+  include:
+    - python: 3.6
+    - python: 3.7
+      dist: xenial  # required for Python >= 3.7 (travis-ci/travis-ci#9069)
+    - python: nightly
+      dist: xenial
+install:
+  - pip install -r requirements.txt
+  - pip install flake8
+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  # add other tests here
+notifications:
+  on_success: change
+  on_failure: change  # `always` will be the setting once code changes slow down