More docs for building/using libwabt?

I wasn't able to find much documentation about libwabt.js, but I was able to piece this together from various sources. Corrections/elaborations are invited.

Usage

Call either parseWat(filename:string, watSource:string, features: object) or readWasm(buffer: Uint8Array, {readDebugNames:true}).

The features object can contain any of the following boolean keys: mutable_globals, exceptions, multi_value, sign_extension, sat_float_to_int, simd, threads, tail_call, bulk_memory, reference_types.

The calls to parseWat and readWasm will return an object wasm that supports the following methods:

• wasm.destroy()
• wasm.resolveNames()
• wasm.validate(features)
• wasm.toBinary({log: boolean, write_debug_names: boolean}): { log: string, buffer: Uint8Array}
• wasm.generateNames()
• wasm.applyNames()
• wasm.toText({foldExprs: boolean, inlineExport: boolean}): string

Updating/Building

The file demo/libwabt.js in the wabt git repository is periodically updated. It's not clear how to do this manually oneself, to incorporate recent changes to the repo. Issue #536 says that this can be done by running make emscripten-release, which uses a target from the repo's top-level Makefile.

However, I just now tried going into my emsdk folder, updating it following the instructions here (including the source ./emsdk_env.sh command), then cd-ing into my wabt repo and trying make emscripten-release. This fails with:

mkdir -p out/emscripten/Release/
cd out/emscripten/Release/ && cmake -G "Unix Makefiles" /Users/jim/Documents/CLOUD/dev/wasm/wabt/ -DCMAKE_TOOLCHAIN_FILE=/Users/jim/Documents/CLOUD/dev/wasm/emsdk/upstream/emscripten//cmake/Modules/Platform/Emscripten.cmake -DCMAKE_BUILD_TYPE=Release 
CMake Error at /Users/jim/_dev/wasm/emsdk/upstream/emscripten/cmake/Modules/Platform/Emscripten.cmake:100 (message):
  Failed to fetch compiler version information with command
  "'/Users/jim/_dev/wasm/emsdk/upstream/emscripten/emcc' -v"! Process
  returned with error code 1.
Call Stack (most recent call first):
  /opt/local/share/cmake-3.16/Modules/CMakeDetermineSystem.cmake:93 (include)
  CMakeLists.txt:18 (project)


CMake Error: CMake was unable to find a build program corresponding to "Unix Makefiles".  CMAKE_MAKE_PROGRAM is not set.  You probably need to select a different build tool.
-- Configuring incomplete, errors occurred!
make: *** [out/emscripten/Release/Makefile] Error 1

Start with demo/libwabt.js, the top-level Makefile, and the emscripten-release target referenced from issue #536. Verify the documented parseWat/readWasm API and investigate the reported emsdk/CMake failure. Done means the usage details and reproducible steps for updating or building libwabt.js are documented.