Aesqlapius

* Queries may now return `Dict` of rows by specified (by either
name or index) column, with possibility to omit key column from
the output.
* Queries may now return single value (scalar) as row type.

* Added global `generate_api()` entry point for all supported
drivers. Driver is now selected by a string argument.
* Replace `file_as_namespace` flag with clearer `namespace_mode`
argument which allows `dirs`, `files` and a new `flat` modes.
* Allow loading queries from a plain file
* Added documentation

* Initial release