Refresh individual posts

It would be nice to be able to regenerate a single blog post. I have 200 posts and it takes ~30 seconds to regenerate when I run:

$ pelican content -o output -s pelicanconf.py

I find myself having to make small corrections often during the writing process and after initial publication when mistakes are discovered. So 30 seconds is added to every iteration.

If just the blog itself, the homepage and indices were the only files being regenerated, something like the following would finish much faster.

$ pelican content/cars/new.rst -o output -s pelicanconf.py