Add CLI::replxx library.

Author: AmokHuginnsson

README.md

@@ -165,6 +165,7 @@ A curated list of awesome C++ (or C) frameworks, libraries, resources, and shiny
  * [gflags](https://gflags.github.io/gflags/) - Commandline flags module for C++. [BSD]
  * [Ncurses](http://invisible-island.net/ncurses/) - A terminal user interfaces. [MIT]
  * [PDCurses](https://github.com/wmcbrine/PDCurses) - Public domain curses library with both source code and pre-compiled library available. [PublicDomain]
+ * [replxx](https://github.com/AmokHuginnsson/replxx) - A readline and libedit replacement that supports UTF-8, syntax highlighting, hints, works on Unix and Windows. [BSD]
  * [TCLAP](http://tclap.sourceforge.net) - A mature, stable and feature-rich library for defining and accessing command line arguments in ANSI C++. [MIT]
  * [termbox](https://github.com/nsf/termbox) - A C library for writing text-based user interfaces. [BSD]