Reddit module

Here's a reddit module that I wrote to watch for new messages and/or submissions. The module depends on the official [Python Reddit API Wrapper](https://github.com/praw-dev/praw) (available through pip/PyPI). The functionality should be mostly self-explanatory; here are a couple of usage examples:

```python
# Watch for and display your unread message count.
status.register("reddit",
    format="{message_unread}",
    username="your_username",
    password="your_password",
    mail_brackets=True)

# Watch for and display rising submissions on your frontpage.
status.register("reddit",
    format="[{submission_subreddit}] {submission_title} ({submission_domain})",
    username="your_username",
    password="your_password",
    sort_by="rising",
    color="#AAAAAA",
    colorize=False)
```
Example output:
![ss](https://cloud.githubusercontent.com/assets/882430/3629156/cd52ac84-0e9c-11e4-8b1c-8534c74faec0.png)

I've also included a minor bugfix to the bitcoin module that prevented price-drops from being properly detected and added an exception block to the shell module to prevent errors in cases of the specified command returning no output.