No reserve command - reserve-with-timeout only option

[divmgl]

Hi @kr. I'm about to fork this library and add the functionality to reserve a job indefinitely.

This was quite a while ago (almost nine years, wow) but I'm wondering if there's a reason why this is omitted from this library? Is the recommendation to not reserve indefinitely and always provide a timeout? Here's the line in question.

https://github.com/beanstalkd/go-beanstalk/blob/master/tubeset.go#L30

[divmgl]

It looks like there's a proposal to get this in: #50.

[divmgl]

I made a beanstalkd client that has reserve. https://github.com/getjackd/go-jackd