Merge pull request #9 from nat-goodspeed/fiber-mt

Document set_scheduling_algorithm().
Merge pull request #10 from nat-goodspeed/fiber-mt

Add notes for algorithm::active() and get_main_id() methods.
update scheduling algorithm as Nad suggested
Update doc for set_scheduling_algorithm() for void return.

Add note to set_scheduling_algorithm() about caller's responsibility to
eventually destroy the passed scheduler object.