Various updates

Changes:
- Parse YAML test descriptor in test262 tests
- Add Window Timers support to shell (enabled with flag)
- Change some visitor classes to use primitives
- Change generated method names to simplify external stack trace filtering
- Add shell flag to disable tail-call handling
- Fix parser bugs in destructuring assignment
- Add TaskSource class to event-loop machinery
- Allow 'int' return type in native functions
- Fix function clone bug in GetCapabilitiesExecutor
- Fix function clone bug in ProxyRevocationFunction
- Only apply replace-i-with-dot workaround if current Java version is affected
- Add test suite for Promise/A+ tests
Add support for exponentiation operator and Array.prototype.contains (ES7)