Adding changes to HttpHelper

- Using empty() instead of != null as its faster ()
- Checking if class property exists before using it to prevent PHP
Notices
- Docs
- Commented out switch cases that have no logic, now they are defaulting
Adding improved logic to all cases.

Now exceptions are concurrent and easily managed.
Using fallthrough in the switch statement.
Merge pull request #8 from tonzof/master

Pull request to handle internal errors from Mozu's API