Some minor documentation fixes in Quaternion
(transplanted from 6172b8f312c2b471ceca5a5e1250883e5a568346)

--HG--
branch : 3.1
extra : transplant_source : ar%B8%F3%12%C2%B4q%CE%CAZ%5E%12P%88%3EZV%83F
Fix traits of Map<Quaternion>, and respectively extend the unit tests
(transplanted from 1da62463d511ea155ba837b6537e5bb9e325bfbc)

--HG--
branch : 3.1
extra : transplant_source : %1D%A6%24c%D5%11%EA%15%5B%A87%B6S%7E%5B%B9%E3%25%BF%BC