Change misclassified method from GET to POST

Here a POST method is more appropriate since we are causing a change to
occur on the server, rather than simply retrieving information.
Change result-type from Twitter to most-recent

Previously the results that were returned by Twitter was a mix of the
most recent and also the most popular results. Unfortunately, we tend to
get a lot of repeated results when a popular tweet has many ReTweets in
a short amount of time. Therefore, we have switched our result-type to
only request the most recent results.
Handle HTTP HEAD requests

HEAD requests are supposed to be identical to GET requests except they
do not return the response body. However, the receiver can always ignore
the response body, so we implement HEAD as an alias for GET.