Library - step one

- Moved REQUEST_BUFFER_CAPACITY from 608.h to cc_encoders_common.h
(after talking with Anshul), since it's only used in cc_encoders_common
and uses the internal ctx structure.
- Moved fatal function to a variable in the init.
- Renamed CC608_SCREEN_WIDTH to CCX_DECODER_608_SCREEN_WIDTH
- Defined "own" bug exit code for fatal function