Include Rankine in imperial units and equivalencies

This is a feature request for the addition of Rankine to temperature units. It is more useful than Fahrenheit in some cases because it is an absolute scale. The conversion between deg_F and degrees Rankine is adding 459.67. See: Rankine Scale

Proposed change in equivalencies (assuming deg_R is Rankine):

def temperature():
    """Convert between Kelvin, Celsius, and Fahrenheit here because
    Unit and CompositeUnit cannot do addition or subtraction properly.
    """
    from .imperial import deg_F
    return Equivalency([
        (si.K, si.deg_C, lambda x: x - 273.15, lambda x: x + 273.15),
        (si.deg_C, deg_F, lambda x: x * 1.8 + 32.0, lambda x: (x - 32.0) / 1.8),
        (si.K, deg_F, lambda x: (x - 273.15) * 1.8 + 32.0,
         lambda x: ((x - 32.0) / 1.8) + 273.15),
        (deg_R, deg_F, lambda x: x + 459.67, lambda x: x + 459.67),
        (deg_R, si.deg_C, lambda x: (x * 1.8) + 491.67, lambda x: ((x-491.67)/1.8),
        (deg_R, si.K, lambda x: x, lambda x: x)], "temperature")

[mhvk]

@DShivansh - sure!

[simpsonchristo]

Yeah, I’d love to give it a try! It’s on my to-do list for next week. @mhvk