Added 3 test methods to test getValue() to TemperatureTest.java

These 3 methods test getValue() for each unit
Fixed the 3 methods so that they have a precision of 1E-6

The professor requested a precision of 1E-6. Also chose a new given
value to better reflect what happens when decimals are present.
Added 3 test methods to TemperatureTest test getUnits()

These 3 methods test getUnits() for each temperature unit. Also modified
a few comments
Add 6 test methods to TemperatureTest to test changeUnits()

The 6 methods test all six possible conversions for changeUnits()
Added and edited some comments

Also changed 20.54 to -20.54 in the getValue() test methods for C and F
to have a more extreme case.
assignment-3