autotools: add support for disabling Klatt (--without-klatt/--with-klatt=no)
autotools: add support for disabling MBROLA (--without-mbrola/--with-mbrola=no)
autotools: add support for disabling libsonic (--without-sonic/--with-sonic=no)
autotools: add support for disabling async command support (--without-async/--with-async=no)
Merge branch 'master' into android
Android.mk: Only build the parts of libespeak that are actually used.