add versioning

docs/sanic/versioning.md

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+# Versioning
+
+You can pass the `version` keyword to the route decorators, or to a blueprint initializer. It will result in the `v{version}` url prefix where `{version}` is the version number.
+
+## Per route
+
+You can pass a version number to the routes directly.
+
+```python
+from sanic import response
+
+
+@app.route('/text', verion=1)
+def handle_request(request):
+    return response.text('Hello world! Version 1')
+
+@app.route('/text', verion=2)
+def handle_request(request):
+    return response.text('Hello world! Version 2')
+
+app.run(port=80)
+```
+
+Then with curl:
+
+```bash
+curl localhost/v1/text
+curl localhost/v2/text
+```
+
+## Global blueprint version
+
+You can also pass a version number to the blueprint, which will apply to all routes.
+
+```python
+from sanic import response
+from sanic.blueprints import Blueprint
+
+bp = Blueprint('test', version=1)
+
+@bp.route('/html')
+def handle_request(request):
+    return response.html('<p>Hello world!</p>')
+```
+
+Then with curl:
+
+```bash
+curl localhost/v1/html
+```