Commit messages for posterity:
* wip transaction schema definition
* test for SchemaObject
* test SchemaObject definions meta property
* schema documentation updates
* test for basic validation
* commit before change to .json file definiton + rst generation
* move to straight .json schema, test for additionalProperties on each object
* add asset to transaction definiton
* remove outdated tx validation
* make all tests pass
* create own exception for validation error and start validating transactions
* more tx validation fixes
* move to yaml file for schema
* automatic schema documentation generator
* remove redundant section
* use YAML safe loading
* change current_owners to owners_before in tx schema
* re-run tests and make correct yaml schema
* fix some broken tests
* update Release_Process.md
* move tx validation into it's own method
* add jsonschema dependency
* perform schema validation after ID validation on Transaction
* Release_Process.md, markdown auto numbering
* remove old transaction.json
* resolve remaining TODOs in schema docuementation
* add `id` and `$schema` to transaction.yaml
* add transaction.yaml to setup.py so it gets copied
* address some concernes in PR for transaction.yaml
* address more PR concerns in transaction.yaml
* refactor validtion exceptions and move transaction schema validation into it's own function in bigchaindb.common.schema.__init__
* add note to generated schema.rst indicating when and how it's generated
* move tx schema validation back above ID validation in Transaction.validate_structure, test that structurally invalid transaction gets caught and 400 returned in TX POST handler
* remove timestamp from transaction schema index
* Add README.md to bigchaindb.common.schema for introduction to JSON Schema and reasons for YAML
* Use constant for schema definitions' base prefix
* Move import of ValidationError exception into only the tests that require it
* Move validate transaction test helper to tests/common/util.py
* move ordered transaction schema load to generate_schema_documentation.py where it's needed
* use double backticks to render terms in schema docs
* change more backticks and change transaction version description in transaction schema
* make details a mandatory property of condition
* Many more documentation fixes
* rename schema.rst to schema/transaction.rst
* Fix documentation for Metadata
* Add more links to documentation
* Various other documentation fixes
* Rename section titles in rendered documentation
* use to manage file handle
* fix extrenuous comma in test_tx_serialization_with_incorrect_hash args
* 'a' * 64
* remove schema validation until we can analyze properly impact on downstream consumers
* fix flake8 error
* use `with` always
