Group commands into section in documentation

They were already mostly in sections, but without headers.  This commit
moves all the commands under new categories in the console_config.md
documentation file.

docs/console_config.md

 # PD Buddy Sink Serial Console Configuration Interface
 
-Version 1.2.0-dev, 2017-09-11
+Version 1.2.0-dev, 2017-10-09
 
 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 runs a configuration
     PDBS) foo bar
     foo ?
 
-### help
+### Miscellaneous
+
+#### help
 
 Usage: `help`
 
 Prints short help messages about all available commands.
 
-### license
+#### license
 
 Usage: `license`
 
 Prints licensing information for the firmware.
 
-### erase
+#### identify
 
-Usage: `erase`
+Usage: `identify`
 
-Synchronously erases all stored configuration from flash.  This can be used to
-restore a device to its default state.
+Blinks the LED quickly.  Useful for identifying which device you're connected
+to if several are plugged in to your computer at once.
 
-Note: The `erase` command is mainly intended for development and testing.
-Stored configuration is automatically erased if necessary when `write` is run,
-and wear leveling is performed as well.  Unless you really know what you're
-doing, there should be no reason to ever run `erase`.
+### Storage
+
+#### get_cfg
+
+Usage: `get_cfg [index]`
+
+If no index is provided, prints the current configuration from flash.  If there
+is no configuration, `No configuration` is printed instead.
+
+For developers: if an index is provided, prints a particular location in the
+configuration flash sector.  If the index lies outside the configuration flash
+sector, `Invalid index` is printed instead.
+
+#### load
+
+Usage: `load`
+
+Loads the current configuration from flash into the buffer.  Useful if you want
+to change some settings while leaving others alone.  If there is no
+configuration, `No configuration` is printed instead.
 
-### write
+#### write
 
 Usage: `write`
 
 negotiated.  The newly configured power is then made available on the output
 connector if it is available from the source.
 
-### load
-
-Usage: `load`
+#### erase
 
-Loads the current configuration from flash into the buffer.  Useful if you want
-to change some settings while leaving others alone.  If there is no
-configuration, `No configuration` is printed instead.
-
-### get_cfg
+Usage: `erase`
 
-Usage: `get_cfg [index]`
+Synchronously erases all stored configuration from flash.  This can be used to
+restore a device to its default state.
 
-If no index is provided, prints the current configuration from flash.  If there
-is no configuration, `No configuration` is printed instead.
+Note: The `erase` command is mainly intended for development and testing.
+Stored configuration is automatically erased if necessary when `write` is run,
+and wear leveling is performed as well.  Unless you really know what you're
+doing, there should be no reason to ever run `erase`.
 
-For developers: if an index is provided, prints a particular location in the
-configuration flash sector.  If the index lies outside the configuration flash
-sector, `Invalid index` is printed instead.
+### Configuration
 
-### get_tmpcfg
+#### get_tmpcfg
 
 Usage: `get_tmpcfg`
 
 Prints the contents of the configuration buffer.
 
-### clear_flags
+#### clear_flags
 
 Usage: `clear_flags`
 
 Clears all the flags in the configuration buffer.
 
-### toggle_giveback
+#### toggle_giveback
 
 Usage: `toggle_giveback`
 
 device needs more power.  Recommended if the Sink is being used to charge a
 battery.
 
-### set_v
+#### set_v
 
 Usage: `set_v voltage_in_mV`
 
 Note: values are rounded down to the nearest Power Delivery voltage unit
 (50 mV).
 
-### set_i
+#### set_i
 
 Usage: `set_i current_in_mA`
 
 Note: values are rounded down to the nearest Power Delivery current unit
 (10 mA).
 
-### identify
-
-Usage: `identify`
-
-Blinks the LED quickly.  Useful for identifying which device you're connected
-to if several are plugged in to your computer at once.
+### Power Delivery
 
-### output
+#### output
 
 Usage: `output [enable|disable]`
 
 ongoing run of Setup mode.  The output is disabled in Setup mode by default,
 and is always enabled in Sink mode.
 
-### get_source_cap
+#### get_source_cap
 
 Usage: `get_source_cap`