Rename some refactored fct

[Geobert]

Here is the follow up of #369 applying your comments!

[Geobert]

@epage : Changing generate_posts code to call the factorised version generate_doc makes excerpt generation fail.
Doesn't make any sense as I've compare the code, and it's the same. Can it be the cloning?

[Geobert]

yeah, the cloning was not a good idea, this is done while rendering excerpt: https://github.com/cobalt-org/cobalt.rs/blob/master/src/document.rs#L312
hence the error.
Wait for CI and if ok, I'll squashed the commit msg :)

[epage]

Looks good. let me know when its squashed.