Fix bit flip for HR2000+
Make seconds requirement explicit
Fix wrong time unit value in init
Fix wrong time unit in QE65000
Merge branch 'integration-time-seconds'
QE65000 fix returned time has wrong value
added class for TEC

Squashed all commits, removed lots of formatting changes
import struct, setpoint at -15 °C
fixed TEC, now working perfectly
cosmetic changes
Modifications to get USB4000 to work:
 * Added USB endpoint definitions to oceanoptics/defines.py
 * Added USB4000 class to oceanoptics/spectrometers/USB4000.py.
   The main change is that the first 1024 pixels are sent over endpoint 6 and the rest over endpoint 2.
   This required rewriting the _request_spectrum() routine.
 * Added references to the USB4000 class to oceanoptics/utils.py
Update README.md
Removed debug print statements.
Added "time_sec" changes to integration_time()
USB4000 inherit from OOBase

Most of the functionality is already implemented in OOBase, no need for
copying.
USB4000 remove __repr__ for now (move to OOBase later)
Revert HR2000+ _packet_func change

This was probably accidental
USB4000 fix import
USB4000 fix order in __init__
Add note about QE65000 TEC