Cleanup gitignore and remove travis config

.gitignore

@@ -5,6 +5,4 @@ code/python-env
 .debris
 _build/
 dist/
-_build/
-build/
 book.html

.travis.yml

@@ -1,21 +0,0 @@
-language: python
-python:
-    - 2.7
-    - 3.6
-branches:
-  only:
-    - develop
-    - first_edition
-    - second_edition
-install:
-    - pip install flake8  # pytest  # add other testing frameworks later
-before_script:
-    # stop the build if there are Python syntax errors or undefined names
-    - time 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
-    - time flake8 . --count --exit-zero --max-complexity=10 --max-line-length=127 --statistics
-script:
-    - true  # add other tests here
-notifications:
-    on_success: change
-    on_failure: always