Add a makefile for helping with style checking and reformatting (#1665)

* Add a makefile

* Add make.bat

* Slightly modify Palm's makefile

* Use make in tox

* Minimise diff and refactor PATHEXT

* Fix a typo in make.bat

tox.ini

@@ -8,7 +8,7 @@ envlist =
     py35
     py36
     docs
-    dev
+    style
 
 [testenv]
 description = Run unit tests with pytest
@@ -31,7 +31,13 @@ commands =
 
 [testenv:style]
 description = Stylecheck the code with black to see if anything needs changes.
+whitelist_externals =
+    make
+setenv =
+    # This is just for Windows
+    # Prioritise make.bat over any make.exe which might be on PATH
+    PATHEXT=.BAT;.EXE
 basepython = python3.6
 extras = style
 commands =
-    black -l 99 --check generate_strings.py setup.py tests redbot
+    make stylecheck