closer to dynamic programming solution

* revised strategy
* get_contig fast implements a prototype new method which can be
extended to all three (now taking the sum, and results match the current
dynamic sum method)
* the use of diagonals has been scrapped
* we now consider future and past self similarity and pull this as a TxW
matrix
* we then run triangles down this matrix and sum/normalize to generate
SC
* this method now runs in O(W^2T) but could easily be made to O(WT)
* by modifying the self similarity matrix on the fly we can extend the
method to contiguity and symmetry (and possibly a diff map)