Removing ind2sub and sub2ind calls
Made elementwise size metafunction usable externally

SOme new funtors requried to behave like elementwise but on a
subset of their nodes. This make possible by passing w/e sub-tree
to the elementwise size computation.
Implemented sub2ind matlab function
Implemented meshgrid Matlab function
Implemented ndgrid Matlab function
Implemented randi Matlab function
Implemented rng Matlab function
Implemented ind2sub Matlab function