Added SQL Server style named parameter.

[ryokash]

Added SQL Server style (i.e. @param_name style) named parameter.

>>> from sqlparams import SQLParams
>>> formatter = SQLParams('named_sqlserver', 'qmark')
>>> formatter.format('select * from Test where id = @id', {'id': 10})
('select * from Test where id = ?', [10])

[cpburnz]

Thanks, this is a useful addition. I'll review it this weekend.

[cpburnz]

v6.2.0 has been released on PyPI.