Unsound usages of unsafe implementation from `u8` to `u32`

[llooFlashooll]

Hi, I am scanning the ewasm_api in the latest version with my own static analyzer tool.

Unsafe conversion found at: src/lib.rs#L258-261

    unsafe {
        native::ethereum_log(
            data.as_ptr() as *const u32,
            data.len() as u32,
            topic_count as u32,
            topic1 as *const u32,
            topic2 as *const u32,
            topic3 as *const u32,
            topic4 as *const u32,
        );
    }

This unsound implementation would create a misalignment issues if the type size of u8s is smaller than the type size of u32.

This would potentially cause undefined behaviors in Rust. If we further manipulate the problematic converted types, it would potentially lead to different consequences such as access out-of-bound. I am reporting this issue for your attention.