added CSP, XFO and STS middlewarez
add Do Not Track middleware
reference to MDN
X-XSS-Protection
X-Content-Options
cosmetic changes and docstrings
code typos
add CSP warning and ref
add CSP report only mode
fix two missing "self."
X-XSS-Protection test case
X-Content-Options test case
X-Frame-Options test case with new syntax
X-Content-Security and Strict-Transport-Security test cases
bug in format() index
test STS for non-None value
correct reference to test against in XSS_PROTECT
Merge branch 'master' of https://github.com/kravietz/django-security.git
X-Xss-Protect just check if it's not None
test for Django version and do not use HttpOnlyMiddleware if >= 1.4
add initial version of Content Security Policy responder