InputStream: use std::string
output/{alsa,oss}: convert to C++
faad.m4: remove faad --with-* options

Some of these are not implemented properly and never worked.  And the
others are not useful; you can easily set environment variables
instead.
faad.m4: don't add -I. to temporary CFLAGS
faad.m4: clear FAAD_LIBS if faad got auto-disabled

Fixes build errors on systems without libfaad, when --disable-aac was
not specified.
decoder/faad: use the newer NeAAC* API

Drop support for the old faacDec* API.
output/osx: convert to C++
test/{read_conf,run_filter}: convert to C++
ConfigFile, CommandLine: use the Path class
require GLib 2.24
ClientSubscribe: remove obsolete typedef
playlist/{asx,rss,soundcloud,xspf}: merge code to MemoryPlaylistProvider
playlist/memory: use std::forward_list instead of GSList
playlist/despotify: various code simplifications
ArchivePlugin: scan_next() returns const string
ArchivePlugin: replace scan_reset(), scan_next() with visit()

Add the interface ArchiveVisitor.
test/visit_archive: new debug program
refcount: convert to C++
ArchiveFile: convert to a class