C(++)->JS Argument binding.

Hi guys,

Something I cannot find anywhere in the documentation is argument binding. You see, I would like to call a JS function dynamically but wish to bind the arguments to a template like EM_ASM does. Obviously I now get an error since the code is not in the consts.
```
#define EM_CALL_EX(...) ((void) emscripten_asm_const_int(call.c_str() _EM_ASM_PREP_ARGS(__VA_ARGS__)))
EM_CALL_EX(5, "test");
```
Is there any way to call a function name dynamically but with a set amount of arguments and types? This is mostly for type safety and such; but also since apparently the speed would improve over the eval() method.

Sincerely,

Start by tracing the emscripten_asm_const_int entry point and the _EM_ASM_PREP_ARGS macro used in the example. Check the existing documentation and implementation for whether dynamically named JavaScript calls with typed, bound arguments are supported. Done would be a decided approach and corresponding documented behavior or implementation, with type safety and non-eval performance requirements addressed.

Scritto dal modello di indicizzazione a partire dal testo della issue.