Qupy

Fixed bug when using GPU

Improvements

- improve code design
- fix code for backward compatibility

Improvements

- improve code design
- further speedup when using GPU 6
- add QFT and IQFT gate

You can now consider the statistical error and phase relaxation in QuPy!

You can now get the expected value of any observable! (use `qupy.qubit.expect`)

Changed:
- method name
- `qupy.qubit.projection` -> `qupy.qubit.project`

fix 1