sqlite-utils duplicate command, closes #454, refs #449

Also made it so .duplicate() raises new NoTable exception rather than raising
an AssertionError if the source table does not exist.

docs/cli-reference.rst

@@ -1176,6 +1176,20 @@ reset-counts
       -h, --help             Show this message and exit.
 
 
+duplicate
+=========
+
+::
+
+    Usage: sqlite-utils duplicate [OPTIONS] PATH TABLE NEW_TABLE
+
+      Create a duplicate of this table, copying across the schema and all row data.
+
+    Options:
+      --load-extension TEXT  SQLite extensions to load
+      -h, --help             Show this message and exit.
+
+
 drop-table
 ==========
 

docs/cli.rst

@@ -1476,6 +1476,15 @@ You can specify foreign key relationships between the tables you are creating us
 
 If a table with the same name already exists, you will get an error. You can choose to silently ignore this error with ``--ignore``, or you can replace the existing table with a new, empty table using ``--replace``.
 
+.. _cli_duplicate_table:
+
+Duplicating tables
+==================
+
+The ``duplicate`` command duplicates a table - creating a new table with the same schema and a copy of all of the rows::
+
+    $ sqlite-utils duplicate books.db authors authors_copy
+
 .. _cli_drop_table:
 
 Dropping tables

docs/python-api.rst

@@ -691,6 +691,8 @@ The ``table.duplicate()`` method creates a copy of the table, copying both the t
 
 The new ``authors_copy`` table will now contain a duplicate copy of the data from ``authors``.
 
+This method raises ``sqlite_utils.db.NoTable`` if the table does not exist.
+
 .. _python_api_bulk_inserts:
 
 Bulk inserts