for cli.rb#timeline: --max_results option and silent-error-handling

It was unclear from the documentation of #timeline that it would accept a `-n` of greater than 200. I suppose we could just add an example to the README making that explicit. I thought maybe just having a flag (`--max-results`) would ease it slightly for the end-user, so they don't have to keep track of what the limit is (as it differs for home_timeline and user_timeline). 

I added one functionality change: if `Collectable#collect_with_count` errors out in the middle of a batch, any tweets collected so far will still be sent to the user. However, the error is swallowed silently. Not sure if that will confuse users by default?

And then there's a bunch of tests, most of them written when I didn't realize what `collect_with_count` was doing cleverly :)