Update offsets within USB read for better precision

"./pcsensor -v" was returning me USB data with the final line (which
includes the measured temperature) like:

80 04 11 11 11 70 00 00

The code was treating byte 2 as the MSB and byte 3 as LSB. From my
limited testing, bytes 2, 3 and 4 are always the same (0x11 in the
example above) and byte 5 is the LSB.

Prior to this patch, I had no meaningful sub-degree precision. Now it
seems nice and accurate and gives the 0.06 degree resolution stated on
the manufacturer's website (accuracy not tested!)

My lsusb gives:
Bus 001 Device 006: ID 0c45:7401 Microdia
I have a Temper1F.
Flush stdout after each write

Ensures timely output when combining the -l option with the 'tee'
command.
Simplify temperature calculation: it's a fixed-point signed number.
Adjust read offsets based on USB product ID string

Added special case for my hardware ("TEMPer1F_V1.3") leaving the default offset
unchanged from the upstream repository.
Merge petervojtek/usb-thermometer
Update README.md
Tidy up some compiler warnings
Merge pull request #2 from petechap/master

Change of byte offset of USB temperature data