Use multiple generator threads when filtering to more than 100 log streams; fixes #82

[mmaslowskicc]

No description provided.

[coveralls]

Coverage increased (+0.2%) to 92.647% when pulling 581ef5c on mmaslowskicc:log-streams-limit into 021691b on jorgebastida:master.

[jorgebastida]

I do like this idea, but I think the code would benefit from a few changes:

• Handle thread termination when the program has to exit.
• Share a deque to avoid duplicated log lines between generators?

If anybody is happy to jump into updating this PR, I'll happily merge it.