Introducing initial states

[Chiffafox]

Adding initial states

[DSGuala]

Are we missing the final " | "?
I don't recommend merging the suggestion, not sure about the formatting.

Suggested change

	| `initial_state_dets` | `dict({float : numpy.ndarray})` | Slater determinants for initial states of varying quality
	| `initial_state_coeffs` | `dict({float : numpy.ndarray})` | Coefficients of Slater determinants for initial states of varying quality
	| `initial_state_dets` | `dict({float : numpy.ndarray})` | Slater determinants for initial states of varying quality |
	| `initial_state_coeffs` | `dict({float : numpy.ndarray})` | Coefficients of Slater determinants for initial states of varying quality