Add a default timeout of 80 seconds for API requests.

The http.DefaultClient has no timeout on requests. In our other bindings,
we set an 80 second timeout. AFAIK this particular value is tied to a
considered funnel of timeouts that works back through our systems.
Use a correct duration for the http.Client timeout
Add a comment explaining the default timeout value
Merge pull request #42 from metcalf/master

Add a default timeout of 80 seconds for API requests.