.add_database() and .remove_database() methods, refs #671

Also made a start on the Datasette class documentation, refs #576

docs/datasette.rst

@@ -0,0 +1,43 @@
+.. _datasette:
+
+Datasette class
+===============
+
+Many of Datasette's :ref:`plugin_hooks` pass a ``datasette`` object to the plugin as an argument.
+
+This object is an instance of the ``Datasette`` class. That class currently has a large number of methods on it, but it should not be considered stable (at least until Datasette 1.0) with the exception of the methods that are documented on this page.
+
+.add_database(name, db)
+-----------------------
+
+The ``datasette.add_database(name, db)`` method lets you add a new database to the current Datasette instance. This database will then be served at URL path that matches the ``name`` parameter, e.g. ``/mynewdb/``.
+
+The ``db`` parameter should be an instance of the ``datasette.database.Database`` class. For example:
+
+.. code-block:: python
+
+    from datasette.database import Database
+
+    datasette.add_database("my-new-database", Database(
+        datasette,
+        path="path/to/my-new-database.db",
+        is_mutable=True
+    ))
+
+This will add a mutable database from the provided file path.
+
+The ``Database()`` constructor takes four arguments: the first is the ``datasette`` instance you are attaching to, the second is a ``path=``, then ``is_mutable`` and ``is_memory`` are both optional arguments.
+
+Use ``is_mutable`` if it is possible that updates will be made to that database - otherwise Datasette will open it in immutable mode and any changes could cause undesired behavior.
+
+Use ``is_memory`` if the connection is to an in-memory SQLite database.
+
+.remove_database(name)
+----------------------
+
+This removes a database that has been previously added. ``name=`` is the unique name of that database, also used in the URL for it.
+
+.plugin_config(plugin_name, database=None, table=None)
+------------------------------------------------------
+
+This method lets you read plugin configuration values that were set in ``metadata.json``. See :ref:`plugins_plugin_config` for full details.