define PROMPT_COLOR
add PROMPT_USERHOST default variable
add colorpre and colorsuf variables
drop PROMPT_ERROR
drop built-in container support for now
reset color after $ prompt
only define default functions if setting PS1

add PROMPT_SEPARATOR and PROMPT_DIRECTORY default variables (#2239152)
add optional PROMPT_START and PROMPT_END (replaces PROMPT_BRACKETS)
add prompt_default(), prompt_traditional(), and prompt_default_os()
expand README.md

add a container ⏢ symbol prefix

add PROMPT_DIR_COLOR to change the dir color (Thomas Steenholdt, #2239152)
also check for bash default prompt for login shell (Sam Morris, #2248853)
add PROMPT_BRACKETS to surround the prompt with traditional brackets

only show error code if PROMPT_ERROR set

rename source package to shell-color-prompt

the colon separator is now uncolored

revert default to normal green (not bright/bold)
set prompt_color_force to override interactive terminal checks
drop bold from red error code

quote TERM expansion in conditional

change default to dim reverse video

initial poc with bold green default