Moves linenoise line editing routines that were originally ported to ELKS bash shell to C library. This allows arrow-key line editing and command line history to be easily added to other applications in ELKS. Astandard (bash-compatible) TAB completion routine is also moved from the shell to libc.

Discussed briefly in #2406 (comment).

To add automatic line editing and tab completion to ELKS applications, instead of using fgets use:

#include <linenoise.h>
...
    // fputs(prompt); fflush(stdout);
    // if (fgets(buf, sizeof(buf), stdin)) do_something(buf);

    linenoiseSetCompletionCallback(linenoiseStdCompletion);
    char *str = linenoise(prompt);
    if (str) do_something(str);
    linenoiseHistoryAdd(line); /* Add to cmdline history */
    linenoiseFree(line);       /* The returned line has to be freed */