White space cleanup

XeroOAuth-PHP most closely adheres to the Zend Framework coding standard, but there are numerous inconsistencies including
   - Extra line breaks at the end of line returns;
   - Missing white space between conditional;
   - Tabs instead of white space;
   - Missing white space padding for associative arrays;

I have corrected these issues in all of the PHP files with the exception of only fixing EOL and tab issues in lib/OAuthSimple.php because that external library does not seem to adhere to the same coding standard.