Merge pull request #58 from dmarkhas/deprecate_pkg_errors

deprecate github.com/pkg/errors

Merge pull request #57 from dmarkhas/err_not_run_yet

Add sentinel error to indicate a check has not run yet

Merge pull request #51 from dmarkhas/sensible_defaults

set default execution period to avoid panic

Merge pull request #39 from dmarkhas/context_support

Added context support

Fixed opencensus dependency on the main project

Merge pull request #32 from bivas/extract-metric-to-listener

Extract metric to own module

Fixed the ability to configure an HTTP check (POST) body payload

fixed a race condition around check results

Removed dependency on a non-standard logging library

upgrade OpenCensus and docs improvements