mp3: Ogg::Vorbis::Header::PurePerl doesn't have a "load" method

This is actually a bug in Ogg::Vorbis::Header::PurePerl. At least, in
its documentation but while it is not properly fixed we can just make
use of the "new" method since both are equivalent.
deps: Updated the pre-requisites to the true minimum

The helper modules to extract the information from the different audio
media types are not hard pre-requisites since Apache::MP3 will only
make use of the ones available.

In addition, the documentation has been updated to make notice that
Apache::MP3 is also available to stream MP4/AAC audio through the
usage of the MP4::Info module and OGG-Vorbis through the alternative
Ogg::Vorbis::Header::PurePerl module.
doc: Updated documentation to state that the demo is not available any more