Simplify settings and file extensions

[ghost]

Jinja does not have a standard file extension, so wouldn't it make sense to just use the file extensions that jinja would be used in by context.

For example, you'll be using markdown, xml, or html files which would be the common types. The jinja docs also specify that you can use j2 or jinja even though they are arbitrary by definition.

The settings are also nothing more than duplicate settings as well even though they all use the same configuration. It makes the first glance look overwhelming and cumbersome even though it's fine and you only need to edit the initial settings.

I use html for my html templates and found it strange that it didn't work out of the box. Looked at the package source and modified the array by adding it and it worked.