Introduces linting (tox/flake8)

Makes sure lint checks are ran before `docker build` so we fail fast.
Currently `flake8` errors are ignored except for `E101` and `W191`.
This will demonstrate the fail fast case.
Next commit will fix these two errors in the code base.

Author: AndreMiras

.travis.yml

@@ -6,7 +6,8 @@ services:
   - docker
 
 before_install:
-  - docker build --tag=p4a .
+  - sudo apt-get update -qq
+  - sudo apt-get install -qq python-tox
 
 env:
   - COMMAND='. venv/bin/activate && cd testapps/ && python setup_testapp_python2.py apk --sdk-dir /opt/android/android-sdk --ndk-dir /opt/android/android-ndk'
@@ -16,5 +17,10 @@ env:
   - COMMAND='. venv/bin/activate && cd testapps/ && python setup_testapp_python3.py apk --sdk-dir /opt/android/android-sdk --ndk-dir /opt/android/crystax-ndk'
   - COMMAND='. venv/bin/activate && cd testapps/ && python setup_testapp_python3.py apk --sdk-dir /opt/android/android-sdk --ndk-dir /opt/android/crystax-ndk --requirements python3crystax,setuptools,android'
 
+before_script:
+  # we want to fail fast on tox errors without having to `docker build` first
+  - tox
+
 script:
+  - docker build --tag=p4a .
   - docker run p4a /bin/sh -c "$COMMAND"

tox.ini

@@ -0,0 +1,15 @@
+[tox]
+envlist = pep8
+# no setup.py to be ran
+skipsdist = True
+
+[testenv:pep8]
+deps = flake8
+commands = flake8 pythonforandroid/
+
+[flake8]
+ignore =
+    E111, E114, E115, E116, E202, E121, E123, E124, E225, E126, E127, E128,
+    E129, E201, E203, E221, E226, E231, E241, E251, E261, E265, E266, E271,
+    E302, E303, E305, E401, E402, E501, E502, E703, E722, E741, F401, F403,
+    F812, F821, F841, F811, W291, W292, W293, W391, W503