Variable names for temperatures could be made consistent

[edbennett]

Currently four conventions are used for variable names for temperatures in episode 08:

• fahrenheit_val and celsius_val (with or without a suffix)
• temp, with no qualification
• temp_c, temp_f, and temp_k
• temp_fahr and temp_kelvin

Is there a reason not to use a single, consistent way of spelling these?

(In particular, temp with no qualifier makes an assumption of Fahrenheit as the default, which is not true outside of North America; see my comment on #1000.)