Add getrlimit(2)

[kpcyrd]

I'm currently looking for a way to increase the maximum number of open file descriptors, it seems there's no crate yet besides the raw syscall in libc.

There was #364 which didn't get merged though due to some other setrlimit related problems.

[asomers]

If you're interested, feel free to pick up the PR and finish it. Also, is this issue titled correctly? "uname -n" has nothing to do with file descriptors.

[kpcyrd]

@asomers you're correct, I keep confusing those two, thanks.

Do I need to implement all of setrlimit to get the PR merged? It seems there have been some problems with other resources unrelated to fds.

My first guess for the api would be:

getrlimit(Resource) -> Result<(Option<usize>, Option<usize>)>
setrlimit(Resource, (Option<usize>, Option<usize>)) -> Result<()>

[LMJW]

Working on this issue, see PR #1302

[rtzoeller]

#1302 addressed this.