Support double & double_complex

[chengbinfeng]

These data types are much more useful in the science caculation. I would like to modify the data type but worry the algorithm cannot support that.

[dblalock]

Hi chengbinfeng ,

Sounds great. Since the operations are approximate anyway, this should just be a matter of writing a wrapper that turns float64 into float32 (ideally fused with the C++ encoding functions, but it shouldn't make much difference unless the matrices are extremely skinny).

EDIT: actually, complex will be much harder...we'd need to rewrite the low-level encoding functions to operate on complex numbers here, as well as define what if even means to cluster or split on complex values in this context.