Add `as.matrix.extmat' function

It was useful for debugging
From 2d to nd
Convolution in C-code
Generalize hweights for higher dims
At last, shaped nD-SSA

New saga begins!
convolve* -> .convolve*
Add special kind for nd-ssa
Add simple finite-rank test for nd-ssa
Add `plot.nd.ssa.reconstruction()` method
Add wide color Barbara
Add a little bit of manual for nd-SSA
Merge pull request #180 from eodus/3dssa_v8

Add nd SSA, yay!