DDlog v0.2: Optimizations + Relation Transformers feature

• Features

  • Relation transformers (experimental)

• Library functions

  • std.string_substr()
  • std.group_set_unions()
  • allocate.allocate_with_hint()
  • tinyset library

• Optimizations

  • Improved differential dataflow arrangement reuse
  • Save memory and CPU cycles by only boxing large values

• C API improvements

  • ddlog_dump_record() - function to pretty-print DDlog records
  • ddlog_dump_ovsdb_delta() - a single function to convert all table updates to JSON