Remove MOTHERBOARD from "due" entry

Also reformat and document

platformio.ini

@@ -1,13 +1,12 @@
 #
-# Project Configuration File
+# Marlin Firmware
+# PlatformIO Configuration File
+#
+# For detailed documentation with EXAMPLES:
 #
-# A detailed documentation with the EXAMPLES is located here:
 # http://docs.platformio.org/en/latest/projectconf.html
 #
 
-# A sign `#` at the beginning of the line indicates a comment
-# Comment lines are ignored.
-
 # Automatic targets - enable auto-uploading
 # targets = upload
 
@@ -27,8 +26,22 @@ lib_deps =
   https://github.com/trinamic/TMC26XStepper.git
   https://github.com/adafruit/Adafruit_NeoPixel.git
   https://github.com/ameyer/Arduino-L6470.git
-default_src_filter = +<*> -<src/config/examples>
 
+default_src_filter = +<src/*> -<src/config>
+
+#################################
+#                               #
+#   Unique Core Architectures   #
+#                               #
+#  Add a new "env" below if no  #
+# entry has values suitable to  #
+#   build for a given board.    #
+#                               #
+#################################
+
+#
+# ATmega2560
+#
 [env:megaatmega2560]
 platform    = atmelavr
 framework   = arduino
@@ -38,6 +51,9 @@ board_f_cpu = 16000000L
 lib_deps    = ${common.lib_deps}
 src_filter  = ${common.default_src_filter}
 
+#
+# ATmega1280
+#
 [env:megaatmega1280]
 platform    = atmelavr
 framework   = arduino
@@ -47,23 +63,32 @@ board_f_cpu = 16000000L
 lib_deps    = ${common.lib_deps}
 src_filter  = ${common.default_src_filter}
 
+#
+# PrintrBoard (Teensy++ 2.0)
+#
 [env:printrboard]
 platform      = teensy
 framework     = arduino
 board         = teensy20pp
 build_flags   = -I $BUILDSRC_DIR -D MOTHERBOARD=BOARD_PRINTRBOARD
-# Bug in arduino framework does not allow boards running at 20Mhz
-#board_f_cpu = 20000000L
+#board_f_cpu  = 20000000L     ; Bug in Arduino framework disallows boards running at 20Mhz
 lib_deps      = ${common.lib_deps}
 src_filter    = ${common.default_src_filter}
 
+#
+# PrintrBoard Rev.F (Teensy++ 2.0)
+#
 [env:printrboard_revf]
 platform    = teensy
 framework   = arduino
 board       = teensy20pp
 build_flags = -I $BUILDSRC_DIR -D MOTHERBOARD=BOARD_PRINTRBOARD_REVF
 lib_deps    = ${common.lib_deps}
+src_filter  = ${common.default_src_filter}
 
+#
+# Brainwave Pro (Teensy++ 2.0)
+#
 [env:brainwavepro]
 platform    = teensy
 framework   = arduino
@@ -72,6 +97,9 @@ build_flags = -I $BUILDSRC_DIR -D MOTHERBOARD=BOARD_BRAINWAVE_PRO
 lib_deps    = ${common.lib_deps}
 src_filter  = ${common.default_src_filter}
 
+#
+# RAMBo
+#
 [env:rambo]
 platform    = atmelavr
 framework   = arduino
@@ -81,27 +109,44 @@ board_f_cpu = 16000000L
 lib_deps    = ${common.lib_deps}
 src_filter  = ${common.default_src_filter}
 
+#
+# Anet 1.0 - Melzi clone (ATmega1284p)
+#
 [env:anet10]
 platform     = atmelavr
 framework    = arduino
 board        = sanguino_atmega1284p
 upload_speed = 57600
 lib_deps     = ${common.lib_deps}
+src_filter   = ${common.default_src_filter}
 
+#
+# Sanguinololu (ATmega644p)
+#
 [env:sanguino_atmega644p]
 platform   = atmelavr
 framework  = arduino
 board      = sanguino_atmega644p
 lib_deps   = ${common.lib_deps}
+src_filter = ${common.default_src_filter}
 
+#
+# Due (Atmel SAM3X8E ARM Cortex-M3)
+#
+#  - RAMPS4DUE
+#  - RADDS
+#
 [env:DUE]
 platform    = atmelsam
 framework   = arduino
 board       = due
-build_flags = -I $BUILDSRC_DIR -D MOTHERBOARD=BOARD_RAMPS4DUE_EFB
+build_flags = -I $BUILDSRC_DIR
 lib_deps    = ${common.lib_deps}
 src_filter  = ${common.default_src_filter}
 
+#
+# Teensy 3.5 / 3.6 (ARM Cortex-M4)
+#
 [env:teensy35]
 platform    = teensy
 framework   = arduino
@@ -111,6 +156,9 @@ lib_deps = ${common.lib_deps}
 lib_ignore  = Adafruit NeoPixel
 src_filter  = ${common.default_src_filter}
 
+#
+# Re-ARM (NXP LPC1768 ARM Cortex-M3)
+#
 [env:Re-ARM]
 platform        = nxplpc
 board_f_cpu     = 100000000L
@@ -121,8 +169,11 @@ lib_ldf_mode = off
 lib_extra_dirs  = frameworks
 lib_deps        = U8glib-ARM, CMSIS-LPC1768
 extra_scripts   = Marlin/src/HAL/HAL_LPC1768/lpc1768_flag_script.py
+src_filter      = ${common.default_src_filter}
 
-
+#
+# Re-ARM (for debugging and development)
+#
 [env:Re-ARM_debug_and_upload]
 # Segger JLink
 platform      = nxplpc
@@ -132,7 +183,7 @@ board_f_cpu = 100000000L
 build_flags   = !python Marlin/src/HAL/HAL_LPC1768/lpc1768_flag_script.py
 lib_ldf_mode  = off
 lib_deps      = U8glib-ARM
-src_filter =
+src_filter    = ${common.default_src_filter}
 extra_scripts = debug_extra_script.py, Marlin/src/HAL/HAL_LPC1768/lpc1768_flag_script.py
 debug_tool    = custom
 debug_server  =