Spymem

* Added new hippocampal bioinspired memory models: CA3 alone, hippocampus with a more bioinspired approach for DG and CA1 layers, and CA3 alone content addressable.
* Changed the internal addressing of models within the library, thus updated the new way of importing models (including previous models).
* Added test for new models.
* Updated the documentation to include the new models.

Added param to control the initial weight of CA3cue-CA3cont synapses, i.e., the possibility of preloading the memory with an initial content predefined by the synapse weights.

Fixed error with cue sizes exact multiples of 2.

Added access to new variables (synapses) of the memory model.

First version of the sPyMem python package. Contains the first hippocampus-based memory model.