Finally stop using few-low-lettered globals; use proper Shellfu compliant
naming instead.

Also have separate variables for use in Bash PS*; these need extra chars
for hinting.

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

 *  use non-conflict function names,

 *  simplify PS1 generation,

 *  close PROMPT_COMMAND setup into function,

Now host/user overrides don't have to be created.