Adds support for calling the manage event API with a golang context

[danmrichards]

Summary

Adds a new ManageEventWithContext function which performs the same task as ManageEvent but allows the caller to supply a context. This context can then be used for request cancellation in the event of a deadline or timeout.

ManageEvent now becomes a wrapper of ManageEventWithContext just passing a background context, the underlying functionality will not have changed.

Reasoning

The current ManageEvent method does not allow this and could become problematic should the HTTP request run slowly. It is preferable to put this control in the hands of the caller, should they want to take advantage of this. If not they can continue to use ManageEvent as normal.

Other Changes

• Fixed some missing error checking when building the HTTP request
• Use the HTTP method constant instead of a string literal
• Fixed package name collision with the bytes variable

[theckman]

I want to get context.Context support into this package for all methods, and so I'm going to close this now and assume we'll align on a path forward in #267.

[danmrichards]

Sure, thanks for the update @theckman