The American Psychiatric Association's newly revised document and ASD definitions are also available through the DSM-5 website: http://www.psych.org/practice/dsm/dsm5
The APA site includes the Table of Contents, notices of recent updates, and a list of emerging Assessment Measures. Updates to the DSM site are ongoing. A Fact Sheet outlining some of the most significant changes to the Autism diagnosis is also available.
A retrospective summary of earlier descriptions and definitions (including DSM-IV-TR) is available at unstrange.com.