Peter M. Groen / CLI11

* refactor: new version of MakeSingleFiles

* fix: use CMake and set version

* Fix internal header include paths.

The extra leading "CLI/" part of include directives prevents the inclusion
of CLI.hpp from a relative directory without an extra -I or /I compiler
directive.

* Fix single header generation script.

Files included with "" should be relative to the header file location first.

* Adding nicer header with LICENSE to single file version

* Adding badges

* Clean up sh files

* Adding explicit in a few places

* More fixes from codacy

* Dropping cmake and clang 5 since they are now in Travis

* Dropping pathlib since it is now unused

* Doxy build

* Folding output and fixing ccache

* Fixes for #8, vars hidden and findPython used

* Adding compat with default python, better defaults