Added sparse FD solver
Moved ajusted solver to seperate function.

Commented out for now
Removed grid.

I wanted to make sure that there was nothing weird caused by the reuse of the tmp grid array.
Playing with exact solution
Updated cell numbers
Switched to solver with corrections.

Old k2 is commented out.
Updated notebooks
Simple optimizations, huge improvement!

The index variables were doubles, the conversion to int was taking an enourmous amount of time. Also, I did not define the cij tmp vars with cdef.
Notebook for optimizing weight and interp functions
Notebook for uniform dist of particles in whole domain.
Added model doc.

Started updating from 1D version, but still needs some work.
Found the magic params for SHM.

Ran on a small problem.
Removed the 1D validation and oscillation descriptions.