Provide more meaningful names for some source files and built artefacts

[Jaifroid]

Currently at least one key source file has a misleading name: demo_file_api.cpp. Likewise, the two most important generated files are simply a.out.js and a.out.wasm. The first should be named something like bindings.cpp (but please advise on the most accurate name in a cpp context). And I would like the generated files to be named libzim-wasm.js and libzim-wasm.wasm, as this would fit with the naming schema of our other Emscripten WASMs in Kiwix JS.

I think I know how to rename demo_file_api.cpp throughout the project, but I am a bit stumped with how to rename the Emscripten output files. I cannot find any parameter that seems to provide the prefix a.out. The problem is that these names are hard-coded in a.out.js, and it would be good to be able to generate ready-to-use files that don't need any internal patching.

@mgautierfr Is this something you can help with?

[mgautierfr]

a.out is the default name for generated file if you don't provide one. Try using the -o option (-o libzim-wasm.js)

[Jaifroid]

Thanks, I managed to work it out in #18.