Draft Mode using a Local Variable

[limarta]

Often when writing blog posts, we need a way to store drafts but hide them during deployment. Currently in Franklin.jl, it is possible to add a file to ignore in config.md to skip the file during the build process. However, this also means serve() will also not display the file. It would be helpful to have a "draft" mode that suppresses pages only at deployment time with a draft=true local variable set. Now if a user wishes to continue editing the page locally, calling serve() locally will still display the page.

Example:

+++
draft = true
+++

# This is a post currently being written but not yet for deployment

Partial content...

[tlienart]

I'm supportive of this, it should be a small addition to be added both here and there: tlienart/Xranklin.jl#254

(for context @limarta , I'm trying to limit feature adds to Franklin.jl as the new version is in prep at Xranklin.jl but it's so huge a rewrite that I'm struggling to bring it over the line, but whatever gets added to Franklin.jl also needs to be added there so I'm trying to limit that and aim for Franklin 0.10.x being something of a LTS).