Added first cut at NEAT Calculations

Added NEAT calculations, cleaned up some code, removed some duplication.
Added data sheets

Added data sheets for the N200 (including most of the sub components),
the square-law detector and NI DAQ.  Resolves issue #20
Added voltage to dBm conversion

Added voltage to dBm conversion for square-law detector.  Fixes issue
#19
Bug fixes

Fixed bug on NEAT calc.  Added a conversion so that the time scales of
the N200 and square law roughly match based on their sample rate.