Add ability to preview themes

lib/preview.bash

@@ -0,0 +1,18 @@
+if [[ $BASH_PREVIEW ]];
+then
+  unset BASH_PREVIEW #Prevent infinite looping
+  echo "
+
+  Previewing Bash-it Themes
+
+  "
+
+  THEMES="$BASH_IT/themes/*/*.theme.bash"
+  for theme in $THEMES
+  do
+    BASH_IT_THEME=$(echo $theme | sed "s/\//\n/g" | tail -1 | sed "s/.theme.bash//")
+    echo "
+    $BASH_IT_THEME"
+    echo "" | bash --init-file $BASH_IT/bash_it.sh -i
+  done
+fi