Jimmy Thrasher Copyright Waiver

I dedicate any and all copyright interest in this software to the
public domain. I make this dedication for the benefit of the public at
large and to the detriment of my heirs and successors. I intend this
dedication to be an overt act of relinquishment in perpetuity of all
present and future rights to this software under copyright law.
Fix some more constexpr issues for clang
Detect Darwin in the Makefile and plan accordingly
Use plain libncurses with Apple
clang.kak: hide clang_completion option
Merge remote-tracking branch 'jjthrash/osx-fixes'
Fix cygwin detection in Makefile
Remove redundant -D that was causing problems on OSX

The prior `mkdir -p` took care of what -D was supposed to do.
Merge remote-tracking branch 'jjthrash/osx-install-fixes'