More metadata options for template authors

[simonw]

See this thread on Twitter: https://twitter.com/simonw/status/952637152797458432

[psychemedia]

To summarise that thread:

• expose full metadata.json object to the index page template, eg to allow tables to be referred to by name;
• ability to import multiple metadata.json files, eg to allow metadata files created for a specific SQLite db to be reused in a datasette referring to several database files;

It could also be useful to allow users to import a python file containing custom functions that can that be loaded into scope and made available to custom templates.

[simonw]

It could also be useful to allow users to import a python file containing custom functions that can that be loaded into scope and made available to custom templates.

That's now covered by the plugins mechanism - you can create plugins that define custom template functions: http://datasette.readthedocs.io/en/stable/plugins.html#prepare-jinja2-environment-env