Adding helpful information in case parsing failed.

I stumbled over 2 slight problems of broken configuration files:

1) It said that a error in my JSON file existed (even though it was a yaml file, parsed by libyaml)
2) It didn't tell me which error occured.

both should be fixed with this PR
Merge pull request #111 from martinheidegger/patch-1

Adding helpful information in case parsing failed.