MKVToolNix v70.0.0 “Caught A Lite Sneeze”

# Version 70.0.0 "Caught A Lite Sneeze" 2022-08-14

## New features and enhancements

* MKVToolNix GUI: the user can now control where the job queue files & the
  preferences INI file are stored via environment variables. If set, the
  variable `MKVTOOLNIX_GUI_STATE_DIR` can point to a directory where the GUI
  stores both the job queue sub-directory and the preferences INI file. If you
  only want to relocate the preferences INI file, you can store the desired
  file name for the INI file in `MKVTOOLNIX_GUI_CONFIG_FILE`. Implements
  #3382.
* MKVToolNix GUI: when adding directories via drag & drop/copy & paste the GUI
  will now offer the user the option to create one multiplex settings tab per
  directory & adding all files from that directory to the corresponding, newly
  created tab. Implements #3371.

## Bug fixes

* mkvmerge: AV1 OBU parser: fixed identifying files that only contain single
  frame. Fixes #3380.
* MKVToolNix GUI: multiplexer: when reading color parameters from identified
  files that are floating point numbers (minimum/maximum luminance, projection
  pitch/roll/yaw) the numbers will be formatted in floating-point notation
  instead of scientific notation as mkvmerge only supports the former. Fixes
  #3368.
* MKVToolNix GUI: multiplexer: color parameters that are floating point
  numbers (minimum/maximum luminance, projection pitch/roll/yaw) will only be
  set to a value during identification if the identification actually contains
  the property, and not to 0 anymore if it doesn't.

## Build system changes

* Several merge requests where accepted that improve compilation on MSYS2 on
  Windows. Note that this build type isn't supported.