allow compilation on x32 bit targets aswell

[arturoc]

hey thanks, it seems like this won't compile on stable cause you can't use features there. do we need that feature for this?

[arturoc]

this will only compile in nightly since it uses a feature. one way to fix it would be to check the size of usize on runtime, like:

mem::size_of::<usize>()

or the size of a pointer:

mem::size_of::<*const c_void>()

[arturoc]

this is fixed now