1. Javascript decoder is now exported as a module using DracoModule()
function that needs to be instantiated on the client.
2. Updated Javascript example applications and README.md
3. Added normalization function to VectorD
4. Added support for converting a single signed value to symbol for
entropy coding and vice versa
5. Minor code cleaning
1. Fixed crasher when dependent attributes were encoded.
2. Improved documentation to PointCloud::AddAttribute() methods
3. Fixed some of the inconsistencies with int64_t vs size_t usage
4. Fixed potential IO problems when the input stream does not start from 0.
