TODO

* Add FFT convolution for shared connections when kernel is badly separable

* Implement Monitor objects to monitior various activities

* Implement Network operators that can be called anytime
  => @every(dt)
  => @random(dt)
  -> done trough clock object

- __getitem__ of connections is not working properly
   1. does not take different src/dst shapes into account
   2. does not handle toric connections for shared connections
   -> done

- Add circular option for connection (might be difficult for dense and sparse)
   -> done for dense and sparse

- Allow shared connections even when src and dst are not the same size
   (use scipy.ndimage.interpolation.zoom)
   -> done, use indexing in place of zoom

- Make sparse and dense kernel building much faster (no idea how yet)
   -> done (see convolution_matrix)