Github: United States Code
the UK parliament basically does this already:<p>here's an example of an act that's been modified:
<a href="http://www.legislation.gov.uk/ukpga/Geo3/41/79?timeline=true" rel="nofollow">http://www.legislation.gov.uk/ukpga/Geo3/41/79?timeline=true</a><p>and an example of a bill going through parliament:
<a href="http://services.parliament.uk/bills/2012-13/financeno4/documents.html" rel="nofollow">http://services.parliament.uk/bills/2012-13/financeno4/docum...</a>