CI: Add TravisCI for code linting with flake8

Although this doesn't implement #16, it addresses the need for checking
code style before merging in changes.
This PR is not meant as an alternative to Black, but rather as an easy
first step towards more comprehensive linting, while offloading the
contributors from setting up anything on their end.

Author: oesteban

.travis.yml

@@ -0,0 +1,16 @@
+# vim ft=yaml
+language: python
+sudo: false
+cache:
+  directories:
+    - $HOME/.cache/pip
+
+python:
+  - 3.6
+
+before_install:
+  - python -m pip install --upgrade pip
+  - pip install "flake8<3.0" flake8-putty
+
+script:
+  - flake8 dmriprep

setup.cfg

@@ -90,9 +90,9 @@ parentdir_prefix =
 [flake8]
 max-line-length = 99
 doctests = True
-exclude=*build/
+exclude=*build/,*/_afq/*
 select = C,E,F,W,B,B950
-ignore = N802,N806,W503,E203
+ignore = N802,N806,W504,E203
 putty-ignore =
     */__init__.py : +F401
     docs/conf.py : +E265