Add an option for limiting the age of collected tweets

[milo-trujillo]

At present we collect the most recent ~2000 tweets from each user, per Twitter API limits. This can give an uneven approximation of a community, since it does not represent "recent" interactions in a true time sense, and will include the most recent tweets from a user even if they haven't tweeted in months.

Propose adding a --maxage -A flag to the script for specifying an integer (or float?) number of days. No tweets older than this threshold will be collected.

Implementation will require adding optional oldestDate argument to acquireTweets, which can take an epoch time stamp. If any tweets older than that timestamp are detected, break out of the for-loop currently at:

SocMap/acquire.py

Lines 101 to 113 in c8e9f40

	for tweet in limit_handled(api, cursor.items()):
	mentions = getMentionsFromText(tweet.text)
	date = tweet.created_at
	text = tweet.text
	source = tweet.user.screen_name.lower()
	if( hasattr(tweet, "retweeted_status") ):
	orig_author = tweet.retweeted_status.user.screen_name.lower()
	rt_count = tweet.retweeted_status.retweet_count
	rt = Retweet(source, text, date, mentions, orig_author, rt_count)
	tweets.append(rt)
	else:
	tw = Tweet(source, text, date, mentions)
	tweets.append(tw)

This will not require any changes to analysis.py, or auxiliary tools, or any new interactions with tweepy.