Solving some issues in https://github.com/culqi/culqi-prestashop/issues/19

[hyperized]

Hi there,

Related to: #19

General fixes:

• Removed redundant use of quotes. " quotes force PHP to parse the string as PHP code and this takes longer. Using ' when dealing with a pure string improves speed.
• Replaced dirname(__FILE__) with simply __DIR__ as this has the same result.
• Notice how most request functions throw errors, but none are caught. They are now documented.
• Optimizing PHP function calls.
• Replacing for with foreach.
• Minor JS + CSS fixes.

I would recommend you open up a new issue for this code to include code styling and if possible switch to composer to maintain your dependencies on things like fsockopen.