more cleanups

[alexanderadam]

Hi @chicobico,

this PR

• adds formatting and a few links to the readme file
• returns proper API error message if no auth_token is given
• validates for presence of an access_token
• autogenerates api_token for specs
• adds guard clauses whereever useful
• replaces SQL fragments with ruby syntax to allow database independence
• uses File.join instead manual (and error prone) path concatenation
• adds some table presence checks to allow painless migration up- and downgrading (had to update schema_plus to make it work for mysql)
• adds json_response spec helper to improve readability
• use correct indention in database.yml files
• add .gitignore

Have a nice week.

PS: did you see my PRs and Issues for the chef repo? If I had to chose then postgres support would be my favorite feature wish.