Use UTF8String instead of Pointer_stringify

[bas-d]

This is part of the fix for #196.

[bas-d]

I think the difference in drop_console is caused by side effects that originate in emscripten. Probably best to fix it properly there before merging these changes. Should work with either drop_console true or false. See emscripten-core/emscripten#8558

[bas-d]

Ok turns out drop_console breaks things because of the way emscripten allows rebinding it with Module.print and Module.printErr. It can be easily fixed by explicitly rebinding these in emscripten.sh of the libsodium repo. I'll submit a PR there. I think we need this one as well because it gives a deprecation warning for Pointer_stringify otherwise.

[jennatuckerdeveloper]

Hi! Are the issues with this commit resolved at this point? It looks like the libsodium.js PR that came from this discussion has been merged.