0.8.3 — Keep decimals for more Twinguard / thermostat readings

• Fixed (#352 follow-up): the same int() truncation behind the Twinguard
  temperature bug also coarsened three other readings the SHC sends as decimals
  — Twinguard humidity and air purity, and the Thermostat II valve
  position. These now keep full precision. The sensors display them rounded,
  so the visible value is unchanged; long-term statistics graphs are smoother.
  Requires boschshcpy 0.4.2.