0.7.3 has breaking changes to 0.7.2

Hello,
Seems like patch versions were used for backward incompatible changes.
Example:

I have the following function that works fine in 0.7.2:

```
def snappy_decompress_stream(in_file, out_file):
decompress_func, read_chunk = snappy_formats.get_decompress_function(snappy_formats.DEFAULT_FORMAT, in_file)
decompress_func(in_file, out_file, start_chunk=read_chunk)
```

The above function doesn't work in 0.7.3
There is no `snappy_formats.DEFAULT_FORMAT` anymore. Looking at the unit tests, it seems `get_decompress_function`is not used and instead a `snappy.StreamCompressor` is introduced.

I'm a little confused about a patch breaking all the above!

Start by comparing the 0.7.2 and 0.7.3 behavior around snappy_formats.DEFAULT_FORMAT and get_decompress_function, then review the unit tests that use snappy.StreamCompressor. The report does not define whether done means restoring compatibility, providing a migration path, or documenting the breaking change, so that outcome needs clarification.

索引モデルが issue の本文から書いたものです。