Support hyperlinks

[LinArcX]

Hi Andre, I like the simplicity of this library. but still, it missed some features.(IMO)

One of them is hyperlinks. currently, we have: pdf_add_link(...), but it's just for linking between pages inside a pdf. but what about web links?

This feature can be beneficial.

[SamWindell]

This one tripped me up too.

From what I can tell, it would be very simple to add it to this library. Use pretty much all the same code as the OBJ_link, except we'd need to store the URI string, and then when rendering we'd output a URI action. So instead of the /Dest [%u 0 R /XYZ %f %f null]\r\n, we'd need:

/A <<\r\n
  /S /URI\r\n
  /URI (%s)\r\n
>>\r\n