JS binding for LoudnessEBUR128 algorithm

[albincorreya]

As mentioned in #27, currently there are no JS bindings for algorithms that expect vector_stereosample type for its inputs or output variables. However, an intermediate wrapper can be made for LoudnessEBUR128 using StereoMuxer algorithm in essentia.

This proposed wrapper could expose the following interface for JS bindings instead of expecting a vector_stereosample type.

LoudnessEBUR128(std::vector<float>& left_channel, std::vector<float>& right_channel, const float hopSize, const float sampleRate, const bool startAtZero);