Using repeated sections in the wasm object file format.

[sbc100]

FYI, I'm hoping to piggy back on this proposal to allow the object format to use a "one section for function" and "one section per segment" approach: WebAssembly/tool-conventions#138

This will allow for simplification of llvm tooling and the linker.

I don't need any conditions, but want repeated sections to be valid, which it sounds like this proposal will allow.