[prompt] pass prompt prams from zprompt_theme

While normally it's a good thing that zsh doesn't auto-expand on spaces,
in this case we want to split on spaces into distinct words, that way
the values are passed to `prompt` in multiple params.

Fixes #178

modules/prompt/init.zsh

@@ -4,5 +4,5 @@
 
 if [[ ! ${TERM} == (linux|*bsd*|dumb) ]] && (( ${+zprompt_theme} )); then
   autoload -Uz promptinit && promptinit
-  prompt ${zprompt_theme}
+  prompt ${(ps: :)${zprompt_theme}}
 fi