Add initial shell theming processor

Uses ANSI escape sequences to switch all open terminals to desired
theme. Does not yet include capability to permanently set themes, since
this would have to be handled either through xresources or dependent on
the individual terminals color settings (e.g. `.config/alacritty.yml`
for alacritty). Needs further investigation.

theme_shell

@@ -0,0 +1,55 @@
+#!/usr/bin/env bash
+readonly dependency=("chriskempson/base16-shell")
+
+path="$1"
+package="$2"
+theme="$3"
+permanent="$4"
+
+file_exists() {
+  if [[ -f "$1" ]]; then
+    true
+  else
+    false
+  fi
+}
+check_tfile() {
+  if ! file_exists "$tfile"; then
+    dbg_msg="$dbg_msg theme $theme for rofi not found.\n"
+    exit 1
+  fi
+}
+
+theme_shell() {
+  dbg_msg="SHELL: $package - "
+  tfile="$path/$package/scripts/base16-$theme.sh"
+
+  check_tfile
+
+  if [[ "$permanent" == "true" ]]; then set_shell_theme; fi
+  switch_shell_theme
+
+  [[ "$DEBUG" == true ]] && echo "$dbg_msg"
+}
+
+switch_shell_theme() {
+  # source "$tfile" -- works, but only for current terminal
+  # ANSI solution from: https://www.reddit.com/r/unixporn/comments/80nidw/bspwm_script_to_change_all_themes_on_demand/duxjw1e/
+  # only we can make use of kempson's scripts and send them to all terminals, so we don't have to manually
+  # sed the colors like sed -nE 's/^(color[0-9|_foreground|_background]+)="(.+)".*$/\1,\2/gp' $tfile
+  for term in /dev/pts/[0-9]*; do
+    # shellcheck source=/dev/null
+    source "$tfile" >"$term"
+  done
+  dbg_msg="$dbg_msg Set theme $theme\n"
+}
+
+set_shell_theme() {
+  dbg_msg="$dbg_msg -- shell theme permanent setting not implemented."
+}
+
+if printf '%s\n' "${dependency[@]}" | grep -q -P "^$package$"; then
+  theme_shell
+else
+  printf "Processor does not work for %s, please use another." "$package"
+fi