add url to the wikipedia article for a longer description

                          libcurl's binary interface

ABI

ABI - Application Binary Interface

  First, allow me to define the word for this context: ABI describes the

  low-level interface between an application program a library. Calling

  conventions, function arguments, return values, struct sizes/defines and

  more.

  For a longer descricption, see

  http://en.wikipedia.org/wiki/Application_binary_interface

Upgrades

  In the vast majority of all cases, a typical libcurl upgrade does not break