Documented some of the firmware changes

The new behavior of `write` has been documented, as well as a high-level
description of the new Setup mode behavior with Power Delivery
communications.

The new `output` command now has documented specifications.  Not a
single line of code has been written for it though, but this is isn't a
release so you shouldn't take everything the documentation file says as
true.

docs/console_config.md

 # PD Buddy Sink Serial Console Configuration Interface
 
-Version 1.0.1, 2017-06-19
+Version 1.1.0-dev, 2017-07-27
 
 The PD Buddy Sink can be put into setup mode by holding the Setup button while
-plugging it into a computer.  In this mode, the device does not perform any USB
-Power Delivery communications, instead running a configuration console over a
-USB CDC-ACM virtual serial port.  This allows the user to change the voltage
+plugging it into a computer.  In this mode, the device runs a configuration
+interface over a USB CDC-ACM virtual serial port in addition to the usual USB
+Power Delivery communications.  This allows the user to change the voltage
 and current the Sink requests, as well as other settings related to the
 device's operation.
 
 leveling is done to ensure long flash life, and the flash sector is
 automatically erased if necessary.
 
+If the output is enabled, the newly written configuration is automatically
+negotiated.  The newly configured power is then made available on the output
+connector if it is available from the source.
+
 ### load
 
 Usage: `load`
 Blinks the LED quickly.  Useful for identifying which device you're connected
 to if several are plugged in to your computer at once.
 
+### output
+
+Usage: `output [enable|disable]`
+
+If no argument is provided, prints the state of the power output (`enabled` or
+`disabled`).
+
+If an argument is provided, sets the output to the specified state.
+
+This command only affects whether the output can be turned on during the
+ongoing run of Setup mode.  The output is disabled in Setup mode by default,
+and is always enabled in Sink mode.
+
 ## Configuration Format
 
 Wherever a configuration object is printed, the following format is used.