To complement the single-file decoder new scripts were added to create an amalgamated single-file of all the Zstd source, along with examples and (simple) tests.

Tested with Xcode/Clang, Visual Studio and Emscripten. Some notes and observations:

• This keeps zstd.h as-is and amalgamates the rest of the code (common, compress and decompress). It's possible to in-line this header file too but for a library it doesn't feel like the best approach.
• Dropping the resulting files into a small project Clang was taking slightly longer (in release builds, which I believe was the LTO, but didn't investigate much because on a larger project it didn't make a difference to multi-CPU compilation). Debug builds wasn't noticeable.
• The resulting binary is smaller than with the many-file version. Around 3% smaller on both Mac and Windows. 3% isn't a lot but it's 3% for free!
• The optimised Wasm build of roundtrip.c (compressing then decompressing data) is an amazing 237kB. This needs further investigation (DCE and LTO are probably doing their thing but it's worth a second look).

As few changes as possible were made to the Zstd source. It's probably worth though:

• A better solution for the CHECK_F macro, probably moving it to the shared fse.h (or error_private.h).
• Either moving the single library to its own contrib folder or renaming the decoder project. It's really easy to make single-file decoder, encoder and full codec now, so the instructions and demos could be expanded to show this.