WISH_RPL (i.e. Right Prompt Lengths), WISH_RIGHT_PS1 are now arrays.
WISH_RPLINE tracks the current line. wish_append_right is called by
wish_append to add to WISH_RIGHT_PS1. If wish_append is called with \n
as text, WISH_RPLINE is incremented. (Current limitation: \n can't be
part of any other string passed to wish_append). Right prompt is now printed
using wish_print_right_prompt which iterates over WISH_RPL and
WISH_RIGHT_PS1. Right prompt size is also calculated in
wish_append_right now.
Set WISH_RIGHT_PLUGINS to be displayed on right.
wish_append is stateful now. Appends to WISH_RIGHT_PS1 or WISH_LEFT_PS1
based on WISH_STATE. wish_append also calculates the length of right
prompt. This has the downside that right prompt can't include any text
that expands on PS1. Therefore, a limitation needs to be applied on
plugins to only append text that won't be expanded in PS1. (i.e. no \u,
\h, \w, \W, etc).