v0.1.0: Add Disease onset field

Please note that this release is not compatible with the 0.0.7 release. There are limited changes which may or may not impact your usage. Notable changes are as follows:

Changed primary Individual name from patient to subject in phenopackets.proto
Added new HtsFile message for capturing High-Throughput Sequencing file information to base.proto
Replaced File vcf and GenomeAssembly in PhenoPacket with repeated HtsFile hts_files in phenopackets.proto
Added Resource.iri_prefix in base.proto
Added Disease.onset field in base.proto

Added new PhenoPacketFormat utility class for converting to/from JSON and YAML