add 'function_index' function, similar to 'function', but returns new position instead of value, and make 'function' use it
change size computation for 'a(b)' to be more like MATLAB. Part of issue #300
adapt relative_index test after change in structure of function node
add optimization for contiguous indexing on terminal
add erase function that removes elements at a certain index in a table
add along_index, like function_index but for along
add erase(a, i, dim) that uses along_index
fix issue with const in nt2::raw
make _() generate a special empty_colon node for easy recognition
add recognization of a(b) = _() to call erase(a, b)