Framework improvements

This is a follow-up of !550 (closed) which intends to improve the framework.

Included improvements:

• fix typos in names
• add comments
• rename outputFormat to outputConfig in decoder.c
• add error return checks in decoder.c
• remove hrtfCRendReaderEnabled and hrtfCRendFileName leftovers
• remove obsolete data type conversion in ivas_fb_mixer_cross_fading()
• add const to ROM tables
• define function ivas_hrtf_init() as global instead of twice as local ones