Update CONTRIBUTING.md
Cache control headers & query string asset management

closes #1470
issue #1405

- added cache control middleware
- added defaults for all routes, assets, etc
- updated asset helper to add a query string with a timestamp hash to all assets
- added unit tests for asset and ghostScriptTags helpers
- added cache-control checks to route tests
Merge pull request #1798 from ErisDS/cache-control

Cache control headers & query string asset management
Move config path.update to config.load

issue #1789

- we can do this step a bit earlier and it aids with neatness
- also means for tests that config.load() is enough to get config & paths initialised
Merge pull request #1813 from ErisDS/path-change

Move config path.update to config.load
Fixing Admin force SSL redirect, adding more options

Fixing SSL redirect handling behind a proxy (`sever.enable('trust
proxy')`). Also fixing handling of Admin theme resources, which should be
served via HTTP when requested.

Adding more options:

  1. Send a non-301 response - for example, 401 Unauthorized
  2. Configure a different hostname for SSL (e.g. 'https://secure.myblog.com')