What's Changed
* ARXML: improve reference handling by andlaus in https://github.com/cantools/cantools/pull/361
* ARXML: consider the choices for the initial signal value by andlaus in https://github.com/cantools/cantools/pull/363
* ARXML: always pretend to be version 4.0 for AR4 by andlaus in https://github.com/cantools/cantools/pull/362
* bitstruct types are pickleable now
**Full Changelog**: https://github.com/cantools/cantools/compare/36.5.0...36.6.0