Debugging: class for delayed one-time debugging_requested() handling
AAC common: convert mxverb() to mxdebug()
bit_cursor_c: fix byte-alignment function
bit_cursor_c: new convenience functions get_remainig_bits(); skip_bit()
build system: avoid certain warnings with clang & libstdc++
Refactoring: rename bit_cursor_c to bit_reader_c
AAC common: fix parsing of AudioSpecificConfig

Actually parse the GASpecificConfig and the ProgramConfigElement if
channel configuration is set to 0.

Fixes #872.