Describe the bug
NuShell native and external commands hang when followed by a newline/linefeed character.

To Reproduce
Steps to reproduce the behavior:

1. Open a text editor.
2. Type ls followed by the Enter key.
3. Copy paste the entire text including the line return to the command line.
4. NuShell will try to execute the command immediately but hang and do nothing.
5. Teste

if you have a command typed as

echo foo \
  bar

that ends up as separate entries in mcfly, rather than a single one. It looks like mcfly is incorrectly parses the history entry? The relevant snippet for that from my .zsh_history is:

: 1593624164:0;echo foo \\
 bar

It looks like mcfly is getting confused by this, and I think it only gets the last line of the comman

.. since italic text ANSI escape codes can cause problems on some terminal emulators / tmux.

Current test code coverage is pretty low (about 13.56%): https://codecov.io/gh/mesalock-linux/mesabox/tree/master

Our target coverage is around 80%.

We currently output completion possibilities over 25 in length by simply joining them with \ns. We should mirror sh style completions and format them into columns.