Better default name for database file

The default name `out.sqlite` is quite generic:

```txt
$ sqlitebiter file test.csv
[INFO] convert 'test.csv' to 'test' table
[INFO] converted results: source=1, success=1, created-table=0
[INFO] database path: out.sqlite
```

Instead, the name should be based on the input filename.

e.g. `test.sqlite`
