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

make.bat

@@ -0,0 +1,30 @@
+@echo off
+
+if "%1"=="" goto help
+
+REM This allows us to expand variables at execution
+setlocal ENABLEDELAYEDEXPANSION
+
+REM This will set PYFILES as a list of tracked .py files
+set PYFILES=
+for /F "tokens=* USEBACKQ" %%A in (`git ls-files "*.py"`) do (
+    set PYFILES=!PYFILES! %%A
+)
+
+goto %1
+
+:reformat
+black -l 99 !PYFILES!
+exit /B %ERRORLEVEL%
+
+:stylecheck
+black -l 99 --check !PYFILES!
+exit /B %ERRORLEVEL%
+
+:help
+echo Usage:
+echo   make ^<command^>
+echo.
+echo Commands:
+echo   reformat                   Reformat all .py files being tracked by git.
+echo   stylecheck                 Check which tracked .py files need reformatting.