Switch to `CBinding@1`

[sloede]

Xref #29.

To make this a non-breaking change, we might want to use the j option to recreate all symbols as before (they are prefixed with p4est_ anyways), see also https://github.com/analytech-solutions/CBinding.jl#options-for-c.

[ranocha]

I'm totally in favor of trying to make this non-breaking.