Support cbor tag range 0x0600-0x06FF once registration is approved

[dlongley]

Tag range 1500-1800, which includes sub-range 0x0600-0x06FF (1536-1791) is to be registered for CBOR-LD use. A flag should be added to optionally use the new tags 0x0600 (uncompressed mode) and 0x0601 (compressed mode) when encoding. The old tags 1280-1281 (0x0500, 0x0501) will still be supported for decoding and used by default for encoding prior to any major release.