Update PostSources to support one level of dir in controller by default

[atiq-cs]

This is a most commonly used setting. It should be enabled by default for convenience if we may.

to support post URLs like,

support /posts/year, for example,

https://blog.corp.com/posts/2011/post-title.html

support /posts/category, for example,

https://blog.corp.com/posts/algorithm/algo-post-title.html

Otherwise, we have to fork theme submodule to make this small change to support mentioned use cases of URL.

Test of the template,

To the contributors, owners and maintainers, thank you for this awesome project :)

[atiq-cs]

@daveaglick what are your thoughts on this?

[daveaglick]

Love this change! Small and powerful, nicely done.