Merge branch 'ps/reftable-api-revamp'

Merge branch 'ps/reftable-api-revamp'

Overhaul of the reftable API.

* ps/reftable-api-revamp:
  reftable/table: move printing logic into test helper
  reftable/constants: make block types part of the public interface
  reftable/table: introduce iterator for table blocks
  reftable/table: add `reftable_table` to the public interface
  reftable/block: expose a generic iterator over reftable records
  reftable/block: make block iterators reseekable
  reftable/block: store block pointer in the block iterator
  reftable/block: create public interface for reading blocks
  git-zlib: use `struct z_stream_s` instead of typedef
  reftable/block: rename `block_reader` to `reftable_block`
  reftable/block: rename `block` to `block_data`
  reftable/table: move reading block into block reader
  reftable/block: simplify how we track restart points
  reftable/blocksource: consolidate code into a single file
  reftable/reader: rename data structure to "table"
  reftable: fix formatting of the license header