The old names ("system" and "application" compression) were not really
accurate in all cases, so the compression types are now referred to by
their number.
The non-stream-based APIs still exist as before and are not deprecated,
they just act as thin wrappers around the stream-based API.
The main rsrcfork module doesn't use the stream-based APIs yet, because
it reads each resource's data all at once and not incrementally.
The decompression code is more readable this way, because the
compressed data needs to be processed sequentially. It also allows
moving the length check and some debug logging into an outer generator.
This also allows incremental decompression, but this doesn't have any
practical advantage, because the compressed resource data is all read
at once (there is no API for opening resources as streams), and
resources are not very large anyway.
The leading underscore is meant to distinguish private (for internal
use only) APIs from public (for external use) APIs. One can argue about
where the line between public and private should be, but if something
is used from other modules (as with read_variable_length_integer) it's
not really private IMHO.
In scripts (like __main__) it also doesn't make much sense to use
leading underscores, because the entire file is never meant to be used
by external code.
All decompressors now have exactly the same signature (as a result,
each decompressor now has to check itself that the header type is
correct). This allows the decompressors to be stored in a simple
dictionary, which makes the lookup process much simpler.
