Remove $pgUA

Formed part of an odd double-system of setting and resetting
the user agent.

People should be using setUserAgent(), which has existed for some
time. Add in a defined() check so HTTP() can be used standalone
/ increased modularity.
Set CURLOPT_PROXY* options once, not every method.

If different proxies are to be used for each request, there should be
a set proxy. Not sure why you'd want to do that though.
Whitespace and misc followup to HTTP class improvements
Merge pull request #55 from Jarry1250/httpclass

Update HTTP() to improve modularity, code reuse