feature: automation of shell settings on alx init

[hiro08gh]

This adds an option to automatically write to the shell configuration file when alx init is run.

alx init

Choose your shell.

Initialized alx configuration at: "/your_alx_path/alx"
Select your shell:
> zsh (default)
  bash
  fis

Choose whether to write the 'alx' alias configuration to your shell file. The default is No.

To enable aliases, add the following line to your shell config:
     # Add to '/your/.zshrc'
     [ -f '/your_alx_path/alx/shell/aliases.sh' ] && source '/your_alx_path/alx/shell/aliases.sh'
Do you want to add this line to '/your/.zshrc' automatically? [y/N]