py-zstandard: update to 0.8.1

0.8.1:
Add #includes so compilation on OS X and BSDs works.

0.8.0:
CompressionParameters now has a estimated_compression_context_size() method. zstd.estimate_compression_context_size() is now deprecated and slated for removal.
Implemented a lot of fuzzing tests.
CompressionParameters instances now perform extra validation by calling ZSTD_checkCParams() at construction time.
multi_compress_to_buffer() API for compressing multiple inputs as a single operation, as efficiently as possible.
ZSTD_CStream instances are now used across multiple operations on ZstdCompressor instances, resulting in much better performance for APIs that do streaming.
ZSTD_DStream instances are now used across multiple operations on ZstdDecompressor instances, resulting in much better performance for APIs that do streaming.
train_dictionary() now releases the GIL.
Support for training dictionaries using the COVER algorithm.
multi_decompress_to_buffer() API for decompressing multiple frames as a single operation, as efficiently as possible.
Support for multi-threaded compression.
Disable deprecation warnings when compiling CFFI module.
Fixed memory leak in train_dictionary().
Removed DictParameters type.
train_dictionary() now accepts keyword arguments instead of a DictParameters instance to control dictionary generation.

(adam)