Provide PTRACE_PEEKUSER API

[alex]

Right now in order to use PTRACE_PEEKUSER you need to directly invoke ptrace::ptrace, which is deprecated. It'd be great if there was a non-deprecated wrapper for PEEKUSER.

[Susurrus]

Indeed, the goal is to get rid of the ptrace() function completely in favor of wrappers, and this would be a most welcome addition. Feature requests are mostly done by volunteer contributors like yourself. Would you be willing to submit a PR providing this implementation?