OTBR Toolbox v3.2.0 — Consistency completed, open trigger counters

Completes the v3.1 consistency work and opens up the MRI trigger counters.

Highlights:
- The Sound and Video modules, getMousePos, getButtonClick, createButton,
  inputTextBox, startQuestionnaire, nBackBuffer, changeTextSettings and the
  MRI functions follow the v3.1 conventions, with many bug fixes found on
  the way (controlSound device and stop, loadSound resampling, initWindow
  under Octave on Windows, ...).
- New: checkSound and checkVideo measure sound and video playback on a
  machine; new options in loadVideo, startVideo and plotScale.
- MRI: the source code of all three trigger counters (Keyboard, Parallel,
  Network) ships with new triggerCounter3 programs; initMRIChatPart1 no
  longer starts a run whose triggers nobody counts.
- Fixes reported by users of 3.1.0: keyBuffer and getAnswer accept Inf as
  duration again; keyBuffer with 'feedbackBad' no longer crashes.

Upgrade notes:
- initMRIChatPart1 stops with an error if the trigger counter is missing,
  misspelt or empty in trigger mode.
- initOTBR rejects stimuli that reach past the edge of the screen.
- All trigger counters need libusb-1.0.dll next to the program.
- Examples need initOTBR.m and VERSION copied from the top level
  (Examples/README.txt).

See CHANGELOG.md [3.2.0] and docs/public_api.md for the full inventory.