Multiple `--skip`s should add together.

Hello.

I have been trying hexyl to explore some wasm files, and as each "section" has a length defined in bytes. For example, the permeable is always 8 bytes, but the next section has its length spelt out. So I wanted to hexyl FILE.wasm -s 8 -s 9 and immediately skip to the next section without pesky manual addition but that didnt work out.

I'd be happy to implement this and send a PR of the implementation.