Correct Fields for PGN 130312

...r PGN 130312 to reflect correct usage of one byte per field

I am waiting on the arrival of a Maretron TMP100 to verify the mapping of temperature source IDs to names. I believe it should look like this, but I'm not 100% on the correct order:

```C
#define LOOKUP_TEMPERATURE_SOURCE ( \
    ",0=Sea Temperature" \
    ",1=Outside Temperature" \
    ",2=Inside Temperature" \
    ",3=Engine Room Temperature" \
    ",4=Main Cabin Temperature" \
    ",5=Live Well Temperature" \
    ",6=Bait Well Temperature" \
    ",7=Refridgeration Temperature" \
    ",8=Heating System Temperature" \
    ",9=Freezer Temperature" )
```