Returns a list of `DBParameterGroup` parameters.
    CLI example to description of parameters ::

        salt myminion boto_rds.describe_parameters parametergroupname\
            region=us-east-1

def describe_parameters(name, Source=None, MaxRecords=None, Marker=None,
                        region=None, key=None, keyid=None, profile=None):
    '''
    Returns a list of `DBParameterGroup` parameters.
    CLI example to description of parameters ::

        salt myminion boto_rds.describe_parameters parametergroupname\
            region=us-east-1
    '''
    res = __salt__['boto_rds.parameter_group_exists'](name, tags=None,
                                                      region=region, key=key,
                                                      keyid=keyid,
                                                      profile=profile)
    if not res.get('exists'):
        return {'result': False,
                'message': 'Parameter group {0} does not exist'.format(name)}

    try:
        conn = _get_conn(region=region, key=key, keyid=keyid, profile=profile)
        if not conn:
            return {'result': False,
                    'message': 'Could not establish a connection to RDS'}

        kwargs = {}
        kwargs.update({'DBParameterGroupName': name})
        for key in ('Marker', 'Source'):
            if locals()[key] is not None:
                kwargs[key] = str(locals()[key])  # future lint: disable=blacklisted-function

        if locals()['MaxRecords'] is not None:
            kwargs['MaxRecords'] = int(locals()['MaxRecords'])

        pag = conn.get_paginator('describe_db_parameters')
        pit = pag.paginate(**kwargs)

        keys = ['ParameterName', 'ParameterValue', 'Description',
                'Source', 'ApplyType', 'DataType', 'AllowedValues',
                'IsModifieable', 'MinimumEngineVersion', 'ApplyMethod']

        parameters = odict.OrderedDict()
        ret = {'result':  True}

        for p in pit:
            for result in p['Parameters']:
                data = odict.OrderedDict()
                for k in keys:
                    data[k] = result.get(k)

                parameters[result.get('ParameterName')] = data

        ret['parameters'] = parameters
        return ret
    except ClientError as e:
        return {'error': __utils__['boto3.get_error'](e)}