Docs for exec pipeline and manifests

- Added manifest logic docs
- More obvious pointers to flushing
- Removed Director page since it duplicated a lot of information already presenting in routing,
which in itself is already duplicated between routing.md and controllers.md.
- Merged Director execution rundown into main exec pipeline docs
- Moved YAML security note from main installation docs to "secure coding", making it sless obvious
Merge pull request #4 from chillu/pulls/exec-pipeline

Docs for exec pipeline and manifests