Provide simple and complex acceptance test cases for YAML front matter.

Alongside with a restructuring of the unit tests for the YAML front
matter, acceptance test cases have been provided. The simple case is
what has been deduced fron unit tests, while the complex case stems from
a real-world example.

Checking in with red test for the complex case.
Merge pull request #10 from ilkerde/develop

Provide simple and complex acceptance test cases for YAML front matter.