TagLibAmalgam: A new way to use TagLib

[Vinnie Falco]

> When compiling the amalgamated file (with clang) I get some (but few) warnings.

I'm working on getting rid of the warnings. Currently I'm doing this
in Visual Studio but once I'm done I will hop on over to Xcode and see
what's going on in there.

Fixing the warnings means submitting a pull request for a change to
the official taglib repository - you can't fix a warning in the
amalgamation, it would have to be done in original source and then
re-amalgamated.

A non virtual destructor could in theory be a problem, if a derived
class is deleted through an alias to its base. Does this happen in
practice? I rather doubt it. But we should still fix it.