Add matrix Redis datatype

* Adds XGET and XSET commands
* XSET rplies with dimensions and shape of matrix
* XGET replies with content of selected subregion of matrix

Shape reply:
* Number of dimensions (dims)
* dims replies for the size of each dimension (shape)

Content reply:
* Number of dimensions (dims)
* dims replies for the size of each dimension (shape)
* product(shape) doubles for each value
Box values in scalar struct for ref counting
Add zero matrix function for initializing with zeros
Slice and set values in subregion
Remove unused function
Add XZEROS and XONES for creating matrices
Reorganize function declaration order
Add XEYE command for creating identity matrices
Add stride argument to matrixSetValues

Dries up creating identitiy matrices
Add stride argument to generic matrix create cmd
Rename getReshapedIndex to reshapedIndex
Add rdb persistence for matrix type