Multiple bug-fixes, primarily for stability

[jdcockrill]

The two commits included cover the 5 issues I've just raised, particularly:

• started adding validation for startATMode (more needed),
• integer HTTP status code return types for get and post,
• correcting Content-Length = 0 check
• adding timeout to readResponse
• disconnecting at the end of get and post

[digistump]

Thanks - this is awesome!