Added route(..), fixed dap_enable(..)

Adding route() made me review dap_enable() more closely and it wasn't
doing what I intended to do before, it was ignoring I2S coming back from
Teensy, DAP was sourced from ADC as was I2S_DOUT and DAC was sourced
from DAP; Teensy received valid data from ADC but data from Teensy was
just discarded if user selected it.
Fix 'no return value' in other route(..);

The alternative route(..) was declared as unsigned short but was not
return anything.
Improve accuracy in AudioPeak(..);

min and max resetting to 0 each reset wasn't as accurate in a shortened
sampling time as making them the opposite of their potential maximums.

removed conditional serial prints as well, they were a hangover from
trying to make AudioInputAnalog & AudioOutputAnalog cooperate in a 'non
standard' order for my current pet project.

Considered renaming Dpp() to what it is abbreviating, being
DataPeak2Peak, but not sure that is a good name anyway.
control_sgtl5000.* overhaul with many renames.

While changing everything else I also modified most things regarding
gain or volume from using 0 to 100 (or -100 thru 0 to 100) to using 1
(or -1 to 1) with only one exception I can think of right now in the
autoVolumeControl(..); - I modified all examples I found .volume or
similar in to suit.

I found opportunity to write these changes, I did not have a chance to
test much more extensively than just compiling it. I will have a chance
to test them by about 24 hours time.
Fixed gain calculator problem

Bit of a fight with the github client, heaps of distraction and no time
delayed me getting back to this. Sorry.
Merge pull request #27 from robsoles/master

Semi automated routing, SGTL members renamed & gain/volume set around 1