Add support for cache tagging

Fix class name

Fix typo

Clean up test

Improve code and add docs

Add another expression example

Add check for characters in tag name that clash with regex

Refactor BanInterface

Rename ban to banPath and implement simpler ban method

Make cache tags HTTP header settable

Add note on dependencies

Re-add cache proxy interface

Make Varnish tests compatible with refactored BanInterface

Make functional test case easier to use

Make separate case for when tags are banned

Fix banning tags and add functional test

Don't flush Varnish if no requests are queued

Add flush expectation

Explain how to configure Varnish for cache tagging

Fix link in docs