title: Regex to exclude all chars except letters
body: <p>I'm a real regex n00b so I ask your help:
  I need a regex witch match only letters and numbers and exclude punctations, non ascii characters and spaces.</p>
  
  <p>"ilikestackoverflow2012" would be a valid string.</p>
  
  <p>"<strong><em>f### you °§è</em></strong>" not valid.</p>
  
  <p>"<strong><em>hello world</em></strong>" not valid</p>
  
  <p>"<strong><em>hello-world</em></strong>" and "<strong>*hello_world*</strong>" not valid</p>
  
  <p>and so on.</p>
  
  <p>I need it to make a possibly complex business name url friendly.</p>
  
  <p>Thanks in advance!</p>