Added datasheet for TPA152 class AB headphone amplifier
Started rev2a design based on rev1a
Lots of things:
--Added RGB LED on timer outputs
--Input: Moved capacitively coupled feedback nodes from vgnd to gnd
--Output: LTC6242 for filtering to amplifier
--Power: 2-stage supply for analog: USB 5V boost to 6V, LDO to 5V
  Digital still using LDO from USB 5V and not caring about anyone
  Bonus! Can completely shut off analog portion of board
--Layout and routing: All of it
TODO: final checks on layout and LVS (vs simulation) HEAD2HEAD2HEAD!
TODO: adjust silkscreen, add logo
TODO: debate adding 12.288MHz dedicated crystal