[hpsdr] piHPSDR on Raspberry Pi 3 B+

[John Ackermann N8UR]

I thought it would be neat to upgrade the processor in my Apache piHPSDR 
console to the new RPi 3 B+.  Its CPU is about 15% faster, and there's a 
big improvement in both wired and wi-fi networking.  The old board 
couldn't quite handle 48 kHz sampling via wireless; I think the new one 
might do it, though I haven't had a chance to thoroughly test yet.

The new board requires an updated operating system image.  I found a 
pointer on the web showing how to do that (it involves magic 
incantations) and have created an SD card image that will work on the 3 
B+ as well as regular 3 B.  It also has the latest release of John's 
pihpsdr software installed, along with some other utilities I downloaded 
to do the updates.

I'm currently uploading the image file to my web site (it's 4.1 GB, so 
takes a while...).  You'll be able to grab it at:

https://febo.com/pages/os_images/2018-07-26_pihpsdr_rpi3B+.zip

It will unzip to a 16GB image file.  Use your favorite tool to write 
that to a 16GB or larger SD card, and you should be set to go.  The 
image is based on the SD card shipped with the Apache Labs phHPSDR 
console, with the updates mentioned above.

73,
John