External renderer: function declarations

The functions declarations for external renderer would benefit from a revision. E.g.

1. Crend: some functions like ivas_rend_initCrend() or ivas_rend_crendConvolver() should be declared as local ones in ivas_crend.c file.
2. Crend: function declaration of ivas_crend_init_from_rom() should be moved from ivas_prot.h to ivas_lib_rend_internal.h
3. TD Binaural Object renderer: majority of functions declarations should be moved from ivas_prot.h to ivas_lib_rend_internal.h
4. Reverberator: functions declarations should be moved from ivas_prot.h to ivas_lib_rend_internal.h
5. Binaural rotator: functions declarations like Quat2Euler(), rotateFrame_shd(), rotateFrame_sd_cldfb() etc. should be moved from ivas_prot.h to ivas_lib_rend_internal.h
6. DirAC renderer prototypes: functions declarations like ivas_binaural_reverb_setReverbTimes() and ivas_binaural_reverb_setPreDelay() should be declared locally in ivas_lib_rend_internal.h

A similar exercise should be done for structures and some files (see VE2AT comments).