Delete extension-specific files using logic

This was taken from my own notes amassed over several years. Commands
like these are a real time-saver.

A lot of people, I imagine, will probably use `-exec rm {} \+` which is
fine and all, but it's another process you'd have to launch, which
isn't necessary at all, unless you need certain `rm` functionality.

sheets/find

@@ -53,3 +53,6 @@ find . -iname '*.txt' -exec vim {} \+
 # Find all files with extension '.png' and rename them by changing extension to
 # '.jpg' (base name is preserved)
 find . -type f -iname '*.png' -exec bash -c 'mv "$0" "${0%.*}.jpg"' {} \;
+
+# Use logic and grouping to delete extension-specific files.
+find \( -iname "*.jpg" -or -iname "*.sfv" -or -iname "*.xspf" \) -type f -delete