Update README.md

Added brief notes on what to do after opening a program in the arduino environment
shutdown is now deprecated, replaced with set_light(,SHUTDOWN_LEVEL,).  OFF_LEVEL also added
shutdown will generate a warning in any debug mode
OFF_LEVEL reassigned to power off, 0 = no light
migrated every reference to shutdown to its direct equivalent with set_light
improved instructions for linux users, recommend arduino 1.0.1 or higher
converted a #ifdef + if(DEBUG== to #if (DEBUG==
fixed a bug in action_timer introduced with the removal of shutdown
added basic light on/off capability to temperature_calibration for running tests.
removed dependency on arduino analogRead, saving 60 bytes
some cleanup for the read_adc conversion
Added a new version of charge_state.

get_charge_state is now redundant, at a cost of 24 bytes.

Previously the charge_value was read on-demand.  It is now read in update().

This means it will incur a cost (of about 50 bytes) to all programs.  This cost could be eliminated with a #define (not implemented).
the placement of read_charge_state causes some stability issues with read_avr_voltage.  I've increased the associated tolerance.
fixed a bug in action_timer introduced by adding OFF_LEVEL
made the library short-circuit on the first run-through of update, we should catch shorter first button presses now
Merge branch 'master' of git://github.com/dhiltonp/hexbright into dev_branch