What's Changed
* ptree <-> QuantumStateBase, ptree <-> json conversion by KowerKoint in https://github.com/qulacs/qulacs/pull/409
* implement ptree <=> operator by KowerKoint in https://github.com/qulacs/qulacs/pull/425
* Implement ptree <=> named gate by KowerKoint in https://github.com/qulacs/qulacs/pull/426
* General Gate <=> ptree by KowerKoint in https://github.com/qulacs/qulacs/pull/433
* matrix gate <=> ptree by KowerKoint in https://github.com/qulacs/qulacs/pull/430
* circuit <=> ptree by KowerKoint in https://github.com/qulacs/qulacs/pull/437
* parametric gate <=> ptree by KowerKoint in https://github.com/qulacs/qulacs/pull/434
* json pytest: operator by KowerKoint in https://github.com/qulacs/qulacs/pull/457
* Json dev copy pauli by KowerKoint in https://github.com/qulacs/qulacs/pull/470
* Json dev gate named test by forest1040 in https://github.com/qulacs/qulacs/pull/463
* Json dev parametricgate by forest1040 in https://github.com/qulacs/qulacs/pull/465
* randomize state by KowerKoint in https://github.com/qulacs/qulacs/pull/476
* Json dev matrix gate test by forest1040 in https://github.com/qulacs/qulacs/pull/467
* Json dev circuit test by forest1040 in https://github.com/qulacs/qulacs/pull/472
* Json dev general gate test by forest1040 in https://github.com/qulacs/qulacs/pull/469
* implement ptree, JSON converting by KowerKoint in https://github.com/qulacs/qulacs/pull/485
* Support for Specifying the Number of Threads using Environment Variables by m-ymzk in https://github.com/qulacs/qulacs/pull/462
* Script to download artifact by ikanago in https://github.com/qulacs/qulacs/pull/490
* Pickle support for quantum state and circuit by kotamanegi in https://github.com/qulacs/qulacs/pull/486
* Use hendrikmuhs/ccache-action to improve cache hit rate by ikanago in https://github.com/qulacs/qulacs/pull/504
* Get embeded qulacs version by Hiroya-W in https://github.com/qulacs/qulacs/pull/492
* fix build warning by KowerKoint in https://github.com/qulacs/qulacs/pull/495
* fix parametric_circuit_from_json by KowerKoint in https://github.com/qulacs/qulacs/pull/502
**Full Changelog**: https://github.com/qulacs/qulacs/compare/v0.5.5...v0.5.6