return response object in case of noop update (paypal#125)

Return response object such that end user can look into what went wrong when the response is nil.

Cases like this occur when there is a no-op update.

Checking previously ignored error which caused issues. (paypal#123)

Error in monitor was going unchecked which caused some issues when the monitor timed out.

Restoring location of r.Close() in retry mechanism since the move cre…

…ated a deadlock. (paypal#122)

Moving the r.Close() call in the retry mechanism created a deadlock since r.Close() also uses the client lock to avoid multiple routines closing at the same time.

This commit reverts that change.

Fixing some cosmetic issues and a potential race condition.

Removing go sum

Since go has launched a checksum database, it is no longer necessary to store go.sum file.
https://blog.golang.org/module-mirror-launch

Moving future to final 0.22.0 release and Mesos 1.6.2 (paypal#114)

Changes in compose testing setup:
* Upgrading Aurora to 0.22.0
* Upgrading Mesos to 1.6.2

Documentation and linting improvements (paypal#108)

* Simplifying documentation for getting started: Removed outdated information about install Golang on different platforms and instead included a link to the official Golang website which has more up to date information. Instructions for installing docker-compose have also been added.

* Added documentation to all exported functions and structs.

* Unexported some structures and functions that were needlessly exported.

* Adding golang CI default configuration which can be useful while developing and may be turned on later in the CI.

* Moving build process in CI to xenial.

* Reducing line size. in some files and shadowing in some test cases.

1.21.0 (formerly 1.4.0) release

Releasing 2.0.1.

Releasing version 1.3.1