Improved readline function to support <- and ->

- readline function now uses raw terminal input mode (if in
interactive session)
- readline function supports cursor movement to the left and to the
right and inline editing (also unicode support)

README.org

@@ -11,7 +11,7 @@ Simple shell for Unix-like systems written in C, that has a funny name (for germ
 - ~cd~ builtin command (~cd~ without arguments moves you to ~$HOME~)
 - ~exit~ builtin command
 - ~CTRL+C~ stops running command
-- Custom ~readline~ function
+- Custom ~readline~ function with support for cursor moving (<-, ->) and inline editing
 - Run scripts with ~arsh /path/to/script~ or by putting ~#!/usr/bin/env arsh~ at the first line of a script and making it executable
 - Run commands with ~arsh -c 'echo $PATH'~ to launch something quickly with ~arsh~.
 * Build