Formatting cleanup in Loader.ts

Preparation for Loader#loadBytes implementation.
Don't overwrite _buffer property set by subclass ctor in DataBuffer ctor
Implement Loader#loadBytes

With trace test.

This shares most code with `Loader#load` by extracting the creation of the parsing worker into a private method on Loader.
Implement Loader#loadBytes

With trace test.

This shares most code with `Loader#load` by extracting the creation of the parsing worker into a private method on Loader.
Merge pull request #1646 from tschneidereit/master

Implement Loader#loadBytes