New report module. 6 persistent work coordinates. New G-codes and settings. README and minor bug updates

(NOTE: This push is likely buggy so proceed with caution. Just
uploading to let people know where we're going.)

- New report.c module. Moved all feedback functions into this module to
centralize these processes. Includes realtime status reports, status
messages, feedback messages.

- Official support 6 work coordinate systems (G54-G59), which are
persistently held in EEPROM memory.

- New g-code support: G28.1, G30.1 stores current machine position as a
home position into EEPROM. G10 L20 Px stores current machine position
into work coordinates without needing to explicitly send XYZ words.

- Homing performed with '$H' command. G28/G30 no longer start the
homing cycle. This is how it's supposed to be.

- New settings: Stepper enable invert and n_arc correction installed.

- Updated and changed up some limits and homing functionality. Pull-off
travel will now move after the homing cycle regardless of hard limits
enabled. Fixed direction of pull-off travel (went wrong way).

- Started on designing an internal Grbl command protocol based on the
'$' settings letter. Commands with non numeric characters after '$'
will perform switch commands, homing cycle, jogging, printing
paramters, etc. Much more to do here.

- Updated README to reflect all of the new features.

Makefile

@@ -1,6 +1,7 @@
 #  Part of Grbl
 #
 #  Copyright (c) 2009-2011 Simen Svale Skogsrud
+#  Copyright (c) 2012 Sungeun K. Jeon
 #
 #  Grbl is free software: you can redistribute it and/or modify
 #  it under the terms of the GNU General Public License as published by
@@ -31,7 +32,8 @@ DEVICE     ?= atmega328p
 CLOCK      = 16000000
 PROGRAMMER ?= -c avrisp2 -P usb
 OBJECTS    = main.o motion_control.o gcode.o spindle_control.o coolant_control.o serial.o \
-             protocol.o stepper.o eeprom.o settings.o planner.o nuts_bolts.o limits.o print.o
+             protocol.o stepper.o eeprom.o settings.o planner.o nuts_bolts.o limits.o \
+             print.o report.o
 # FUSES      = -U hfuse:w:0xd9:m -U lfuse:w:0x24:m
 FUSES      = -U hfuse:w:0xd2:m -U lfuse:w:0xff:m
 # update that line with this when programmer is back up: