This allows a `config.toml` (or `yaml`, ´yml`, or `json`) in the theme to set:
1) `params` (but cannot override params in project. Will also get its own "namespace", i.e. `{{ .Site.Params.mytheme.my_param }}` will be the same as `{{ .Site.Params.my_param }}` providing that the main project does not define a param with that key.
2) `menu` -- but cannot redefine/add menus in the project. Must create its own menus with its own identifiers.
3) `languages` -- only `params` and `menu`. Same rules as above.
4) **new** `outputFormats`
5) **new** `mediaTypes`
This should help with the "theme portability" issue and people having to copy and paste lots of setting into their projects.
Fixes#4490
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
