Enable all supported amendments in Env by default. Rename `features()` to `with_features()` and add `all_features_except()` to support feature subsets in Env. Refactor internal feature handling based on a bitset.
* Remove `src/test/support/mao` * Flatten `src/test/support/jtx` to `src/test/jtx`
Migrate ticket-test.js to cpp. Add coverage for Change/Cancel ticket handlers.
