ncurses 6.1 - patch 20200118

+ expanded description of XM in user_caps.5
+ improve xm example for xterm+x11mouse, xterm+sm+1006 -TD
+ add history section to curs_slk.3x and curs_terminfo.3x manpages.
+ update alacritty entries for 0.4.0 (prompted by patch by
  Christian Durr) -TD
+ correct spelling errors found with codespell.
+ fix for test/configure, from xterm #352.