Hello Guix!

This is a patch to update taglib. I've had to enable building as a
shared library otherwise gst-plugins-good would fail to link. Also,
`guix lint' warned about the home page redirecting to http://taglib.org
so I thought I'd fix that too.

Finally, I tried to enable the tests by adding "-DBUILD_TESTS" as a
configure flag but they are explicitely disabled if building the shared
library:
~~~
if(BUILD_TESTS AND NOT BUILD_SHARED_LIBS)
  enable_testing()
  add_subdirectory(tests)
endif()
~~~

Oh well, how does this look?

Thanks!
Pierre