Translate function pointers and lambda

[lucic71]

Sub-part of #3, only covers: translate function pointers and non-capturing lambdas as Option in unsafe and FnPtr in refcount

• deleted the fn_ptr! macro, address is computed inside FnPtr::new using the FnAddr trait
• replaced cast_history with the original function pointer + current cast
• in unsafe function pointers + casts are translated using: Option<fn> + std::mem::transmute
• in refcount function pointers + casts are translated using: FnPtr<fn> + FnPtr<fn>::cast