synopsis: Fix broken links in Tutorial documentation.
issues: #1206

description: {

    In servant/doc/tutorial/Client.lhs, several links point to an .lhs file,
    which show as broken in the live web documentation. Changing the suffix to 
    .html displays the correct documentation.

    In servant/doc/tutorial/Authentication.lhs, a link to GHC documentation for
    Type Families pointed to a 404'd page. A link to existing GHC documentation
    was substituted.
}