0.2.0: Merge pull request #3 from fakeshadow/atomic

Note since 0.1.0:

Remove:

• remove all 3rd party dependencies.

Changes:

• Can run on any async runtime.
• Manager trait is tasked with runtime specific implementation with Manager::spawn and Manager::timeout for spawning tasks and cancel timedout futures.
• Pool::run returns PoolRef in closure.
• Default scheduled interval tasks are separate from the pool as ScheduleReaping and GarbageCollect trait. They rely on ManagerInterval trait for runtime specific implementation.(In order to make them work they have to be maually hooked on the pool with Manager::on_start)
• Various changes for examples
• Reduce heap allocation

Add:

• no-send feature for a single thread pool.
• Pool::get_owned for get a connection with no direct reference of Pool.
• Pool::pause for pause the pool.
  Pool::resume for resume from pause.
  Pool::clear for clear the pool.
  Pool::set_max_size for set max pool size at runtime.
  Pool::set_min_idle for set min idle pool size at runtime.
• Manager::on_start and Manager::on_stop trait method which would be called on the pool start and stop(drop).