Add static site support

[radiac]

Add a command to build a static site from your script.

I don't want to overload nanodjango with the kitchen sink, but this feels like a very useful feature - I've got several small static sites which I really wanted some of Django's features for, but setting up a full Django project felt overkill. A nanodjango script with a couple of models and some templates would have been perfect.

Probably should depend on #35

Usage: nanodjango <new_command> script.py /path/to/site. Possible command name:

• staticsite - most descriptive, if a bit long (I know I'll type static-site at some point)
• static - shorter, but could confuse people with django's static files (ie nanodjango static .. vs nanodjango manage .. collectstatic)
• build - not specific to building a static file - could conflict with some sort of asset build command, should that ever be needed
• publish - implies deployment, remote server

Possible libraries to base it on, in order of github star popularity:

• django-distill (436 stars). Uses paths so should be easy.
• django-bakery (405 stars, but known use on a big site). Requires class based views, which is fine but complicates things a bit - looks like we can't just dynamically create a view class with a BuildableMixin, seems people would need to explicitly use CBVs, which I'm not wild about
• django-freeze (93 stars). Looks like a reliable package, if a bit newer. Working with a sitemap or HTML links would give us a lot of options.
• There are others, but the ones I've used previously seem to be abandoned.

It looks like some of these packages will also deploy to s3 etc. That'd be a pretty handy feature, but I'm not keen on adding two commands for this. If supported, it would be better as eg nanodjango staticsite s3://...

It may also be good to have a --watch option - but only if there's a significant difference to nanodjango run

One other common use case would be to be running nanodjango serve on a private url, and have changes automatically trigger a build to a public one. That would be a nice feature, but I suspect out of scope - probably best handled with a HOWTO in the docs (touch a file, watch a file?)

Unless anyone has further suggestions, this will be pip install nanodjango[staticsite], nanodjango staticsite <script> <path>, and be based on django-distill, or django-freeze if we run into problems with distill

[radiac]

Thinking about this more, this may make more sense as a separate project. It's definitely something I still want, but it feels like more of an edge case than mainstream, and I'm trying to be mindful of not letting nanodjango get too fat (see #35). It may require an extension of the convert plugin system, or swapping to pluggy.

It could still be installed as a dependency with nanodjango[staticsite], but I'm not sure about it as that would mean installing it with nanodjango[all]. I'm thinking about the learning journey someone's going to go on - once they land on the docs page about creating a static site, it's just as easy to say "now pip install something-else" as it is "I hope you installed with pip install nanodjango[all]"

An additional thought - one of the big problems with this idea is needing to commit the database. Alex Kerney pointed out the yamldl project, which may be a good solution.