This plugin is designed to provide a uniform method of cleanly applying
style modifications to shell information included in the prompt.
Provided in this version are functions to add simple shell parameters
(as in `man zshparam`) with corresponding prefix and suffix
configuration settings, to allow for clean application of style
directives (i.e. color and spacing) as settings rather than directly
inline in your PROMPT.
EXAMPLE THEME USAGE:
...
PROMPT+="$(command_number)"
...
SHELL_PLUGIN[command_number_prefix]="%{$bg[white]%}%{$fg_bold[grey]%} "
SHELL_PLUGIN[command_number_suffix]=" %{$reset_color%}"
