Release v0.2.0

First release checkpoint of Variant Transforms! Main features of this release:

• Highly scalable import of VCF files to BigQuery (500K+ files, TBs of data)
• Robust import functions (see --infer_undefined_headers and --allow_incompatible_records)
• Annotation support (experimental). Add --annotation_fields when running the pipeline.
• See README and documents under the /docs folder for more details.

P.S. We're starting from 0.2.0 instead of 0.1.0 as the initial version at launch should have been 0.1.0.