Moved Common.mk functions back into Arduino.mk which fixes AUTO_ARDUINO_...

[sej7278]

...DIR calculation, which fixes issue #147 allowing much simpler user Makefiles e.g.

BOARD_TAG = atmega328bb
ISP_PROG = usbasp
include /usr/share/arduino/Arduino.mk

Fixed ARDMK_FILE arduino.mk capitalisation

I know it was nice to externalise some common functions but there weren't many and one at least wasn't working and required workarounds in the main Arduino.mk

[sej7278]

do not merge, seems to break ARDMK_DIR and ARDMK_PATH detection:

-------------------------
Arduino.mk Configuration:
- [AUTODETECTED]       CURRENT_OS = LINUX 
- [COMPUTED]           ARDMK_DIR = /usr/share (relative to Arduino.mk)
- [COMPUTED]           ARDMK_PATH = /usr/share/bin (relative to ARDMK_DIR)
- [AUTODETECTED]       ARDUINO_DIR = /usr/share/arduino 
- [AUTODETECTED]       ARDUINO_VERSION = 105 
- [USER]               ARDUINO_SKETCHBOOK = /home/simon/programming/c++/arduino 
- [BUNDLED]            AVR_TOOLS_DIR = /usr/share/arduino/hardware/tools/avr (in Arduino distribution)
- [COMPUTED]           ARDUINO_LIB_PATH = /usr/share/arduino/libraries (from ARDUINO_DIR)
- [DEFAULT]            ARDUINO_CORE_PATH = /usr/share/arduino/hardware/arduino/cores/arduino 
- [COMPUTED]           ARDUINO_VAR_PATH = /usr/share/arduino/hardware/arduino/variants (from ARDUINO_DIR)
- [COMPUTED]           BOARDS_TXT = /usr/share/arduino/hardware/arduino/boards.txt (from ARDUINO_DIR)
- [DEFAULT]            USER_LIB_PATH = /home/simon/programming/c++/arduino/libraries (in user sketchbook)
- [USER]               BOARD_TAG = atmega328bb 
- [COMPUTED]           OBJDIR = build-atmega328bb (from BOARD_TAG)
- [ASSUMED]            MONITOR_BAUDRATE = 9600 
- [DEFAULT]            OPTIMIZATION_LEVEL = s 
- [DEFAULT]            MCU_FLAG_NAME = mmcu 
- [DEFAULT]            CFLAGS_STD = -std=gnu99 
- [AUTODETECTED]       Size utility: AVR-aware for enhanced output
-
-                      ARDUINO_LIBS =
- [USER]                 Adafruit_Sensor
- [USER]                 Adafruit_BMP085
- [USER]                 DHT11
- [USER]                 RF24
- [USER]                 OneWire
- [USER]                 DallasTemperature
- [USER]                 jeelib
- [SYSTEM]               Wire
- [SYSTEM]               SPI
- [SYSTEM]               Wire/utility
- [COMPUTED]           BOOTLOADER_PARENT = /usr/share/arduino/hardware/arduino/bootloaders (from ARDUINO_DIR)
-------------------------