add tox && use black and pylint

.gitignore

@@ -1,4 +1,5 @@
 venv/
+.tox/
 dist/
 assm/__pycache__
 images/

.pylintrc

@@ -0,0 +1,2 @@
+[BASIC]
+good-names = e

assm/__main__.py

@@ -1,5 +1,6 @@
 """iOS splash screen generator"""
 
+import sys
 import os
 from PIL import Image
 from assm.devices import APPLE_DEVICES
@@ -26,7 +27,7 @@ def make_splash_image(screen_orientation, screen_width, screen_height, logo_path
         if str(e) == 'bad transparency mask':
             print('ERROR: Bad transparency mask.')
 
-        quit(-1)
+        sys.exit(-1)
 
     return splash_image
 
@@ -51,9 +52,9 @@ def main(output_folder='./images/'):
 
         try:
             splash = make_splash_image('portrait', device_w, device_h, 'logo.png')
-        except FileNotFoundError as e:
+        except FileNotFoundError:
             print('ERROR: File logo.png not found.')
-            quit(1)
+            sys.exit(1)
         splash.save(file_name)
 
         print('...splash for {w}x{h} saved...'.format(w=device_w, h=device_h))

dev_requirements.txt

@@ -1,3 +1,4 @@
 black==20.8b1
 flit==3.0.0
 pylint==2.7.1
+tox==3.24.0

tox.ini

@@ -0,0 +1,12 @@
+[tox]
+isolated_build = True
+envlist = py36,py37,py38,py39
+
+[testenv]
+deps =
+    black
+    pylint
+    pytest
+commands =
+    black assm --skip-string-normalization
+    pylint assm