The CELT library version 0.6.1 is used including git patch "0f0da999ae82a2b73974cc73a1a19d79a23ba8cd"
of celt.c by Jean-Marc "Better fading for PLC: no fading for the first loss, muting after 6".

Basically the files in celt-0.6.1/libcelt are used.

Changes made to libcelt to be compatible to llcon:

- replaced all "restricted" by "__restricted" and all "inline" by "__inline"