Added slugify (#286)

Co-authored-by: Isabelle Viktoria Maciohsek <maciv@hotmail.gr>

snippets/slugify.md

@@ -0,0 +1,24 @@
+---
+title: slugify
+tags: string,regex,intermediate
+---
+
+Converts a string to a URL-friendly slug.
+
+- Use `str.lower()` and `str.strip()` to normalize the input string.
+- Use `re.sub()` to to replace spaces, dashes and underscores with `-` and remove special characters.
+
+```py
+import re
+
+def slugify(s):
+  s = s.lower().strip()
+  s = re.sub(r'[^\w\s-]', '', s)
+  s = re.sub(r'[\s_-]+', '-', s)
+  s = re.sub(r'^-+|-+$', '', s)
+  return s
+```
+
+```py
+slugify('Hello World!') # 'hello-world'
+```