Information to return codes added to projects and users documentation.

Documentation is updated with information how to handle snippets or how to access tags
and commits. Nearly all project specific functions are now described in the documentation.
A few previous entries have been updated with status codes, e.g. `401 Unauthorized`.

The API documentation for projects now is structured into major sections that describe
the different aspects when dealing with projects, e.g. hooks, branches, team members etc.
All described methods now contain a list of possible status codes the method can return. A few
methods have extra sample JSON responses and a description if a method is idempotent.
Idempotent methods can be called multiple times while returning the same status code.

correctly describes the new behavior

Added documentation for getting project hook and editing project hook.

[ci-skip]

Merge branch 'master' into non-interactive-aws-install

Conflicts:
	doc/installation.md

Fix merge mess in installation.md