`const` option on pointers and slices themselves

[esthedebeste]

the difference between

int *a; // a is a mutable pointer (can be moved) to a mutable integer (can be changed)
int *const b; // b is a constant pointer (cannot be moved) to a mutable integer (can be changed)
const int *c; // c is a mutable pointer (can be moved) to a constant integer (cannot be changed)
const int *const d; // d is a constant pointer (cannot be moved) to a constant integer (cannot be changed)

currently cannot all be represented.

a: int32* := ...; // a is a constant pointer (cannot be moved) to a constant integer (cannot be changed)
b: int32* .= ...; // b is a mutable pointer (can be moved) to a mutable integer (can be changed)

are all we can represent at the moment.