create constant for default database name in sql adapter
create test app for testing pre-loaded sql dbs
Add pre-loaded db support for sql adapter
models/sql_preload test app
let dev know when they use an invalid db file name
skip first migration if using a pre-loaded sql db
add db_name parameter to control database name
add db_name and comments to models/sql_preload
removed down() calls and added preload message
updated README.md