Added async queue and sender

Other changes
- Begun adding yard comments
Added tests for the async queue and sender

Other changes
- Switched time units to seconds for consistency
Updated documentation for async channel
Merge pull request #1 from Microsoft/features/async_sender_and_queue

Features/async sender and queue
Added documentattion for channel classes

Other changes
- Hooked in Yard into Rake
- Small cahnges to README.md for it to look better in the generated docs
- Added additional development dependencies to gemfile
Removed nil check

Other changes
- Removed tests checking for the nil check
Updated documentation for TelemetryClient
Merge branch 'features/documentation' into develop