Renamed Pointer#memcpy and Pointer#memmove to copy_from and move_from. Also added copy_to and move_to.

Add Ubuntu dependencies. Use --run instead of &&

Added Slice and use that in IO. For now there are no extra checks. Also: fixed some things in the compiler and added Enumerable#join(separator, io, &block)

Raise errors on more cases, like duplicated argument names, type var names, reopening a generic class with other type vars, etc.