Http::mapStringOrError could provide more information about status on error

[tonowie]

include more information about server response in thrown exception. Can use also hierarchy of exceptions as part of issue #105

[tonowie]

alternatively if there is a way to better handle informational responses or redirects then it might be worth looking into. at the time of execution of that method it is too late to handle informational responses or redirects though as it is uses in response body processing.

[tonowie]

bb6779d added response code to the exception message reported on failure