Changed
- Breaking: renamed public types to spell out abbreviations, matching the
Zstd<Compress|Decompress><Stream|Parameter>family and zstd's own prose
("compression context", "dictionary"):ZstdCompressCtx→ZstdCompressContext,
ZstdDecompressCtx→ZstdDecompressContext,ZstdCompressDict→
ZstdCompressDictionary,ZstdDecompressDict→ZstdDecompressDictionary.