ape: make version-dependent decoding functions called via pointers

This will help in supporting old versions, e.g. version 3.93 uses the same
range coder but different predictor and version 3.82 uses different range
coder and predictor. Also this should not make decoding newer versions slower
by introducing additional checks on versions.
ape: provide two additional bytes in buffer for old MAC versions

Range coder in 3.90-3.95 overread two bytes in the final normalize.
add support for Monkey's Audio versions from 3.93