Add suport section ID 12 and its respective test

[felipemarts]

I tested the following code compiled using assemblyScript

export function add(a: i32, b: i32): i32 {
  console.log("test add");
  return a + b;
}

the generated wasm file has section id 12 - "data count" which is not yet supported by wasm-json-toolkit.
I took the liberty of adding testing and code to support the same.

Thank you in advance Felipe Martins de Lima.