Add .save command

[asdine]

Add .save command to Genji CLI

Synopsis: .save ?badger? PATH

Description: Write database into PATH

Usage:

# run in memory database
genji
# or on-disk database
genji my.db

genji> CREATE TABLE foo;
genji> INSERT INTO foo(a) VALUES (1);
genji> .save foo.db
genji> .save badger foo 

$ ls
my.db foo.db foo/

Calling .save on an existing database file or path overwrites it.

[asdine]

cc @jhchabran, pinging you so I can assign you

[jhchabran]

You can assign me now 👍