Replaces g_strstrip().

Prepare to migrate away from GLib.  Currently, we're still using GLib
as a backend.

Reduce heap allocator overhead.

Use only ConfigData.hxx in plugin sources to reduce header
dependencies.

Replaces GLib's GError.

g_file_error_quark() is meant to be used with the GFileError enum
which does not correspond with errno, but must be converted with
g_file_error_from_errno().

At the same time, this removes g_strerror() use for
g_file_error_quark().

Make sure we get a UTF-8 encoded string.

Use _scan() instead, to have more control.

The new method pair() receives an arbitrary name/value pair.  Support
for this is being added to a few decoder plugins.

Pass a callback table to scan_file() and scan_stream(), instead of
returning a tag object.

Loop over all frames with a specific id, and import all of them - not
just the first one (index 0).

Add the flag "b" to fopen().  Windows compatibility.

If we define id3v1_encoding, then the tags are not added to the
database.

Allow RIFF/AIFF ID3 tags up to 4 MB (old limit was 256 kB).  This
might still be too small for some users, and when somebody complains,
we might do something more clever (like streaming the data into
libid3tag?).

After we've been hit by Large File Support problems several times in
the past week (which only occur on 32 bit platforms, which I don't
have), this is yet another attempt to fix the issue.