0.68.0

Release notes

Enhancements

• Added MetadataEncoder::encoded_len() for the number of bytes encode() will write
• Added DbnMetadata_encode and DbnMetadata_encoded_size to the C API for encoding
  metadata, including symbols, symbol mappings, and every symbology field
• Added SType to the generated C header
• Improved documentation for the min_price_increment_amount and inst_attrib_value
  fields

Breaking changes

• Removed encode_metadata from the C API. Use DbnMetadata_encode, which takes a
  DbnMetadataRef describing the full metadata rather than only the dataset, schema,
  and start