Use new CBOR tags, restructure registry system.

[wes-smith]

• Restructure term registry system to be more general with four tables which
  can all be passed by the user during encoding and decoding:
  • keywordsTable: for JSON-LD keywords (e.g. '@context', '@type')
  • stringTable: for JSON-LD string values. This subsumes 'appContextMap',
    as context strings can be included here, but includes arbitrary string
    values as well.
  • urlSchemeTable: for URL schemes (i.e. 'http://')
  • typedLiteralTable: for values associated with JSON-LD types. This
    subsumes type-specific codecs like the cryptosuite codec.
• Restructure CBOR-LD tag system to use a range of tags where
  the tag value informs what values for the tables above should be used
  via a registry. Legacy tags (0x0501) are still supported, and new tags are
  in the range 0x0600-0x06FF. In addition, the tag value is part of a varint
  that begins the CBORLD paylaod if necessary that allows for more registry
  entries than the number of tags in that range.