Make svc api more rusty

[roblabla]

the current svcs are basically a copy paste from libt, and are very C-like. I would love to turn them into something closer to rust, and would probably be possible without too much trouble.

We coudl use naked functions and inline asm to recode them. This gives us additional flexibility if we want to make the API more rusty.

Related to #11

[roblabla]

Moved SVC api to naked functions. API is still not very rusty though.

[roblabla]

The new svc functions have a big problem: they don't mark the clobbers/input/output. This is UB, and is causing big problems in release mode. I had hoped that marking them "extern" would be enough, but alas, rust eagerly optimizes everything.

I have a new svc macro, I'm in the process of porting everything to it:

macro_rules! define_svcs {
    ($($(#[$meta:meta])* $name:ident ( $id:expr, ($($svc_name:tt($svc_id:tt)),*), ($($svc_in:tt)*), $($args:tt)* ) -> $return_type:ty;)*) => {
        $(
            $(#[$meta])*
            pub unsafe fn $name($($args)*) -> $return_type {
                let mut ret: $return_type = ::std::mem::uninitialized();
                asm!("svc $0" : $($svc_name(ret.$svc_id)),* : "i"($id), $($svc_in)* : : "volatile");
                ret
            }
        )*
    };
}

define_svc! {
    /// Sets the size of the heap. Equivalent to a brk syscall on unix.
    ///
    /// Note that you should almost never use this method! Use the system
    /// allocator instead, like Box, to allocate heap memory!
    /// @brief Sets the size of the heap
    ///
    /// @param outAddr Output for address of the heap
    /// @param size Size of the heap
    set_heap_size(0x01, ("={x0}"(0), "={x1}"(1)), ("{x1}"(size)), size: u32) -> (Result, *mut cty::c_void);

    /// Sets memory permissions. Takes the address of the region to reprotect,
    /// its size, and the new permission of that region.
    ///
    /// Address and size must be page-aligned, and execute bit is not allowed.
    set_memory_permission(0x02, (), ("x0"(addr), "x1"(size), "x2"(permission)), addr: *mut cty::c_void, size: u64, permission: u32) -> Result;
}