Most notably, add example of Vim configuration needed for the function
to work.

First, I'm not sure where I took the former icon, but it does not work
out of the bos on Fedora, so I decided to use another one rather than
try to find out.

Also when a system is accessed via SSH, it will use different
(fa-server) icon.

How come I haven't set this years ago?

New version aims to simplify main vault and support deeper merging
strategies.  We'll see...

http://unix.stackexchange.com/questions/72131/detecting-x-session-in-a-bash-script-bashrc-etc/338862#338862

Silly but for now it will suffice.  Maybe one day I'll learn the magic
of systemd so that I'll be able to set this up in a less embarrassing
way.

When case is left without quotes, Vim's default syntax highlighter shows
the left bracket in strong, error-y red style (not sure why, e.g.
ShellCheck does not complain about that notation).  It seems to work
fine when quoted, though.

Hardly needed to do repeatedly and when it is, it's best linked with
an observed command on the same line.

Separate declaration from initialization and add variable comments.

I keeo forgetting to say "modify" and even `m` alias did not help.  This
maybe...

...yep, we're getting a bit naggy...

This likely breaks hostname setting when accessing via SSH, but:

 *  it's first version that is at least somehow readable,

 *  and also WE *MAY* have fixed the long-standing PITA escaping
    errors that we used to get in urxvt if BASH_COMMAND had backslashes
    in it!

 *  Remove excess comments and optional syntax (eg. EOL `;`),

 *  use non-conflict function names,

 *  simplify PS1 generation,

 *  close PROMPT_COMMAND setup into function,