DDK Examples made compatible to work with DDK v2.x

+ Added DDK dependent code in ddk.h and changed Examples to use the abstraction
+ Mentioned the DDK jumper usages wherever relevant, esp for serial usage
+ Updated the missing CLCD connection info note, wherever CLCD is being used,
	except the serial, jtag, parallel programmers, where CLCD use is optional,
	though it is enabled by default
+ Generalized the DDK specific comments, wherever possible, to make the examples
	generic. And added DDK specific comments, wherever necessary to mark it
	non-generic
+ Alongwith enhanced the Makefile to support build all. That triggered changes
	into rules.mk & LDDKFirmware Code's Makefile
+ And so based on all the above, took this opportunity to re-organize the Examples
	into various AVR &/or DDK buckets through Makefile and with the ATmega* tag in
	their comment headers. Triggered by compiling these individual buckets:
	. Fixed some compilation warnings & potential bugs
	. Made some examples compatible with more AVRs (fan.c, stepper_motor.c)
	. Noted the further needed cleanups as TODO comments in the Makefile
+ Added new examples triggered by support for DDK v2.1
	. blink_led.c
	. switch_n_ir.c
	. rtc_clcd.c (using rtc.[ch], twi.[ch])
	. rtc_serial.c (using rtc.[ch], twi.[ch])
	. menu.c
	. led_array.c
	. clock.c
	. feature_test.c
	where the last four are specifically for DDK v2.1 only
+ Alongwith adding the long checkin-pending new examples:
	. pwm2.c
	. jana_gana_mana.c (using notes.h)
	. ask_rf_ind_rx_tx.c
	. ir_over_serial.c, ir_send_recv.c, ir_remote.c
	. l293d.c
	For details of todo status of each, check out the Makefile TODO comments
+ Fixed/Got working the following old pending examples:
	. flash_demo.c (using flash.c, flash.h, serial.c, serial.h)
+ Other minor fixes / updates
	. Cleaned up redundant code in switch_n_led.c
	. Added missing header in possible_freq.txt
+ And finally, added a README file with a brief description about this
	folder and how to use these examples with DDK v2.1
Added info on how to use the DDK Examples with the earlier DDK v1.1

+ Updated the README with the relevant information. With this the latest
revision of Examples tree, could be used with all DDK variants, with
appropriate flags, as explained in the README.
+ To achieve this multi-version support, the key change required was in the
commandline of the bootloadHID, i.e. to support downloading the hex code to
different DDK (bootloader) versions based on the options passed to it.
+ Once done with that change, the appropriate options have been actually
passed in the invocation of the bootloadHID commandline through the relevant
make files (Examples/Makefile, rules.mk).