move `shopt` into ansi_filter, closes #1

shlide

···
 }
 
 # Filter out color sequences.
-shopt -s extglob
 ansi_filter() {
+    shopt -s extglob
     local IFS=
     printf '%s' "${1//$'\e'[\[(]*([0-9;])[@-n]/}"
     #" A little fix to prevent vim syntax highlighting from breaking.
+    shopt -u extglob
 }