Handle optional succeeding three letter currency codes

The relevant HTML of the omate pledge page (https://www.kickstarter.com/projects/omate/omate-truesmart-water-resistant-standalone-smartwa/pledge/new) looks like:

    <input alt="$10.00 USD" class="radio" id="backing_backer_reward_id_1910694" 
    name="backing[backer_reward_id]" title="$10.00 USD" type="radio" value="1910694" />

which results in 

    Traceback (most recent call last):
      File "kswatch.py", line 152, in <module>
        rewards = ks.process(url)
      File "kswatch.py", line 65, in process
        self.feed(html)   # feed() starts the HTMLParser parsing
      File "C:\Python27\lib\HTMLParser.py", line 114, in feed
        self.goahead(0)
      File "C:\Python27\lib\HTMLParser.py", line 158, in goahead
        k = self.parse_starttag(i)
      File "C:\Python27\lib\HTMLParser.py", line 322, in parse_starttag
        self.handle_startendtag(tag, attrs)
      File "C:\Python27\lib\HTMLParser.py", line 404, in handle_startendtag
        self.handle_starttag(tag, attrs)
      File "kswatch.py", line 79, in handle_starttag
        self.value = float(attrs['title'][1:].replace(',', ''))
    ValueError: invalid literal for float(): 10.00 USD

This pull request also removes the succeeding three letter monetary code.