Adapt code to archive DMs

* Add argument to get DMs
* Adapt statuses_portion()
* Adapt statuses() to optionally handle DMs
* Adapt main() to pull down DMs if instructed
Allow storage of date in ISO (RFC 3339) format
Convert archiver.py and follow.py to API 1.1

This is mostly done. I've not yet decided on a tidy way to re-implement
the API limit tests, since this has changed significantly between API
versions 1.0 and 1.1.

Further, as I understand it, API 1.1 requires OAuth for everything, but
it is still an optional command argument which is off by default. This
should be fairly trivial to fix, but I've not yet done so.
Add mattcen as author
Fix style of exception handler

http://docs.python.org/2/tutorial/errors.html#handling-exceptions

"except ValueError, e: was the syntax used for what is normally written
  as except ValueError as e: in modern Python (described below). "
Tidy up timestamp and timezone code
Fix timezone bug introduced in previous commit

Removed too much code; wasn't converting to local timezone anymore
Merge pull request #156 from mattcen/master

DM archiving, Twitter API upgrade, better timestamps.
You know what's awesome? Patching a program, realising you should rebase your patch on the latest commit (I based off twitter-1.8.0, so had a fair few changes to make), and then finding all the features (namely Favourites and Mentions) that got added to master in the meantime! Love your project! I will likely try to tweak the Favourites and Mentions behaviours in the near future though so they and Timeline-fetching aren't mutually exclusive.

NOTE: You'd need to update your Twitter App settings to allow viewing and posting of DMs for this to work out of the box for people.

    Add argument to get DMs
    Adapt statuses_portion()
    Adapt statuses() to optionally handle DMs
    Adapt main() to pull down DMs if instructed
    Enforce Twitter API 1.1 for archiver and follow.
    Add option to allow more accurate timestamps (specifically the timezone specification) in output files.