All config variables starts with low-case and uses camelCase.
If there is abbreviation at the beginning of the name, the whole
abbreviation will be written in low-case.
If there is abbreviation at the end of the name, the
whole abbreviation will be written in upper-case.
For example, rssURI.
This is needed to verify #2309, but it closes a big hole in Hugo's automated tests.
The loading of the config is now moved to `hugolib` and the same default settings are now used
in production and tests.
As Viper now uses Afero as its filesystem, we now can write fairly complete integration tests with ease.
See #2309
