v1.0.0-preview7

This release fleshes out the Ptr structs by marking them as readonly and adding all of the comparison operators (>, >=, <, <=), arithmetic operators (+, -), and casting operators that you would expect/need for pointers. Indexers are also now provided. There's now a Value property on each struct, which permits you to pass a pointer into an iterator or into async code and use it (using Get() wouldn't work since it returns a pointer). ToString() methods are provided which default to hex notation (e.g. 0x123456789ABCDEF), and IFormattable is also implemented.