[BUG] Modify default table argument

[davidkurilla]

After implementing the new table functionality and unit tests, reading from the TOML file without a table produces an error. I would like to propose a solution to this issue. The default value for the toml_table argument should be the name of a default table that refuel will search for unless otherwise specified. I would like to propose that the default table be called database. This way the user can ether set up their TOML file with the table database for the default or alternatively can specify a custom table name.