Private Schema and other private methods and constructors

Is there a reason why the convenience object Schema is private?

`private[timeseries] object Schema`

For instance:

```
// preferred but not working because Schema private
val tsRdd = TimeSeriesRDD.fromRDD(sc.parallelize(data, defaultNumPartitions), Schema("time" -> LongType, "id" -> IntegerType, "price" -> DoubleType))(isSorted = true, timeUnit = TimeUnit.NANOSECONDS)

val schema = StructType(
StructField("time", LongType) ::
StructField("id", IntegerType) ::
StructField("price", DoubleType) :: Nil)
val tsRdd1 = TimeSeriesRDD.fromRDD(sc.parallelize(data, defaultNumPartitions), schema)(isSorted = true, timeUnit = TimeUnit.NANOSECONDS)
```

Also, some TimeSeriesRDD constructors are private, which may be useful:

```
private[timeseries] def fromSeq(
sc: SparkContext,
rows: Seq[InternalRow],
schema: StructType,
isSorted: Boolean,
numSlices: Int = 1
): TimeSeriesRDD

private[flint] def fromOrderedRDD(
rdd: OrderedRDD[Long, Row],
schema: StructType
): TimeSeriesRDD = {
val converter = CatalystTypeConvertersWrapper.toCatalystRowConverter(schema)
TimeSeriesRDD.fromInternalOrderedRDD(rdd.mapValues {
case (_, row) => converter(row)
}, schema)
}
```
Also for testing access to the OrderedRdd is valuable, but that is also private

`private[flint] def orderedRdd: OrderedRDD[Long, InternalRow]`

This may open the implementation too much.