Clean up and add existing code

[jonwilsdon]

The code that is currently running the Ion Binary Explorer on the gh-pages branch is not in the main branch of this repository. Copy it to this repository, and clean it up in a series of pull requests.

PRs:

• IonTypes, TypeDescriptorReader, ByteBufferReader (Adds support for reading type descriptors. #10)
• ElementReference, IonElement, ScalarValueReader (ElementReference, IonElement and ScalarValueReader #12)
• SymbolTable, Verifier?
• worker-coordinator, top-level-worker?
• reader-worker, inspect-worker, Inspector, StructuralAnalyzer?