[SPARK-2759][CORE] Generic Binary File Support in Spark

The additions add the abstract BinaryFileInputFormat and BinaryRecordReader classes for reading in data as a byte stream and converting it to another format using the ```def parseByteArray(inArray: Array[Byte]): T``` function.
As a trivial example ```ByteInputFormat``` and ```ByteRecordReader``` are included which just return the Array[Byte] from a given file.
Finally a RDD for ```BinaryFileInputFormat``` (to allow for easier partitioning changes as was done for WholeFileInput) was added and the appropriate byteFiles to the ```SparkContext``` so the functions can be easily used by others. 
A common use case might be to read in a folder 
```
sc.byteFiles("s3://mydrive/tif/*.tif").map(rawData => ReadTiffFromByteArray(rawData))
```
What if we just added a toArray to PortableDataStream, and had only one method for reading these? Then you could do `sc.binaryFiles(...).map(_.toArray)` if you want to get byte arrays. Or would this cause a regression?

Basically my suggestion is to have binaryFiles, which will return an RDD of PortableDataStream, and binaryRecords, which will return an RDD of byte arrays of the same length (since I imagine there's no point streaming a record).