Update getTweets.php

Minor edits to vibeometer.ino
Changes to getTweets:
-instead of doing $nowTime - $tweetTime over and over again, that value
is stored in $timeDiff
-made the query strings better, or at least analogous to those the
apogee console spat out
-changed some of the timing parameters regarding whether a tweet should
be counted
-retweets (with "RT" in them, at least; that seems to be all of them)
are filtered out of the counts