contour 0.2.0.171 rc2

Changes since rc1

• change versioning scheme, adding 4th component to reflect current CI run number
• Last-resort font fallback to shape each grapheme cluster individually to increase success rate
• VS16 always having width 2
• configuration log messages improved
• glitch in box drawing arcs fixed
• revive Alt + mouse button input mapping with a temporary workaround
• Fixes some XTSMGRAPHICS properties.
• Changed "Bright black" RGB color from #000000 to #707070.
• Set default terminal size to 80x25 (was 130x30).
• Mac OS/X: Default shell changed to login -fp $USERNAME (was: login shell as reported by getpwuid($uid)