SDI-12 USB adapter manual updated

I have just finished an update to the SDI-12 USB adapter documentation.

Updates:

1. I added a document to the manual: Sensor connection guide. It lists a number of SDI-12 and other sensor wiring information from various manufacturers. Find it in the SDI-12 USB adapter page under documentation.
2. All sections are now numbered now for easy reference.
3. Two new sensors have been tested by customers to work perfectly with the adapter: Campbell Scientific CS650 and CS655 soil sensors.
4. I added an appendix to explain how to use external power for your SDI-12 sensors, in case they don’t work with the 5V power supplied by the SDI-12 USB adapter. A wiring diagram is included.
5. I added an appendix to explain how to easily connect a Decagon SDI-12 sensor with a stereo plug with a picture.