Pytalises

* added better error messages
* added new tests
* Rabi oscillations
* free propagation
* harmonic oscillator
* added var_pos method to Wavefunction class
* added 2D Gaussian beam example to docs

* added better error messages
* added new tests
* Rabi oscillations
* free propagation
* harmonic oscillator
* added var_pos method to Wavefunction class
* added 2D Gaussian beam example to docs

fixed bug in state_occupation

* fixed bug in freely_propagate method

- bug fix in kinetic operator

* New fft methods for Wavefunction class (9)

* fft method switched to wavefunction

* Delta_t to delta_t

* fixed static time bug