Merge pull request heetch#88 from heetch/add-avrotest

Merge pull request heetch#86 from heetch/057-fix-canon-empty-struct

avro: fix canonicalization

Merge pull request heetch#83 from heetch/051-clean-avdl-comments

cmd/avrogo: better handling of IDL comments

Merge pull request heetch#78 from heetch/049-better-avroregistry-error

avroregistry: better error message on non-JSON response

Merge pull request heetch#77 from heetch/048-empty-records

support empty Go struct types

Merge pull request heetch#72 from heetch/046-retain-logical-types

allow retaining logical types in CanonicalString

Merge pull request heetch#71 from heetch/043-better-struct-defaults

better support for struct-field-typed record field defaults