purge static file cache on new version, closes #12, prerequirement for #13

uffd/template_helper.py

 import random
+import subprocess
 from datetime import timedelta, datetime
 
-# debian ships jinja2 without this test...
-def equalto(a, b):
-	return a == b
-
 def register_template_helper(app):
+	# debian ships jinja2 without this test...
+	def equalto(a, b):
+		return a == b
+
+	@app.url_defaults
+	def static_version_inject(endpoint, values):
+		if endpoint == 'static':
+			values['v'] = app.jinja_env.globals['gitversion']['longhash'] #pylint: disable=no-member
+
 	app.jinja_env.trim_blocks = True
 	app.jinja_env.lstrip_blocks = True
+
 	app.add_template_global(random.randint, name='randint')
 	app.add_template_global(datetime, name='datetime')
 	app.add_template_global(timedelta, name='timedelta')
 	app.add_template_global(min, name='min')
 	app.add_template_global(max, name='max')
 	app.add_template_global(equalto, name='equalto')
+
+	# get git commit
+	GITOUTPUT = subprocess.check_output(['git', "log", "-g", "-1", "--pretty=%H#%h#%d#%s"]).decode('UTF-8').split('#', 3)
+	app.jinja_env.globals['gitversion'] = {'hash': GITOUTPUT[1], 'longhash': GITOUTPUT[0], 'branch': GITOUTPUT[2], 'msg': GITOUTPUT[3]} #pylint: disable=no-member