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.