Updated requirements for php 5.3
Merge pull request #1 from infusionsoft/develop

Updated requirements for php 5.3
Merge branch 'develop'
Updates on requirements. Specify minimum PHP version and extensions from Guzzle in our own composer.json for clarity.
Update README.md

fixed spelling error in the example code showing how to use the logging.
Add DataService.getUserInfo with a flag to not include the empty key parameter.
Reset the needsEmptyKey flag after every request so it doesn't break subsequent calls.
Updated EmailService to be APIEmailService as that's the proper name in the API.
Fix a couple PHPDoc annotations.
Add note about where the clientId and clientSecret come from.
Pass single struct parameter for InvoiceService::validateCreditCard. Fixes #5.
Change return type on API methods to mixed by default.
Annotate requestAccessToken method with exceptions thrown.
Fix some typos in variable names and PHPDoc blocks.
Annotate class variable in test.