ISO 80000-8: Add Octave and Decade units for logarithmic frequency range quantity

[ronaldtse]

Information from ISO 80000-8:

Quantity: logarithmic frequency range
Quantity symbol: G
Quantity definition:

G = "lb"(f_2/f_1) " oct" = "lg" (f_2/f_1) " dec"

Units: Octave "oct" / Decade "dec"

Notes:

One octave (stem:["oct"]) is the logarithmic frequency range between stem:[f_1] and stem:[f_2] when stem:[f_2/f_1 = 2]. Similarly, one decade (stem:["dec"]) is the logarithmic frequency range between stem:[f_1] and stem:[f_2] when stem:[f_2/f_1 = 10]; thus stem:[1 " dec" = ("lb" 10) " oct" ~~ 3.322 " oct"].

Original issue: https://github.com/metanorma/iso-iec-80000/issues/25