implement an "ignore_future" plugin

[willkg]

Need to implement (and enable by default) a plugin that removes entries with mtimes that are in the future so they don't get rendered unless explicitly referenced.

It might be interesting to list them all in future/ kind of like drafts.

[willkg]

Ugh. There's no good way to do this with the existing processing model. The problem is that a bunch of plugins use tools.walk to get a list of all the things in the blog, but that returns a list of file paths and you can't determine from those file paths what's a blog entry in the future or not without opening each file, parsing it and reading the published_date. That's a whole lot of work that's then thrown away.

I think I'll toy with reworking walk so that it runs the results through a callback letting plugins add to or remove items. That'll be a messy callback, but walk is pretty messy. We really want a "get_entries" tools function. Maybe I'll implement that first.

Then implement an ignore_future plugin that looks at a data file to see which file paths were published when and nixes anything in the future. It can call filestat on each file path that isn't in the data file.

[willkg]

Implemented in 6667e262caa1f6fc26fcd0ba0e99e98672268af5

It's easy to use--just add it to the load_plugins list.

However, to implement this, I had to do a bunch of reworking of the internals, so it's possible I broke some things.