seqr: make sequencer multi-threaded

Has multiple threads call run on the io service.

Fixes #6

Signed-off-by: Noah Watkins <noahwatkins@gmail.com>
Merge pull request #13 from noahdesu/make-seqr-multithreaded-6

seqr: make sequencer multi-threaded

Signed-off-by: Noah Watkins <noahwatkins@gmail.com>