Google-Voice-PHP-API Updates

Hey aaronpk,

I used this API a couple years ago to send DJs from my radio station reminders 10 minutes before their show was supposed to start. Then Google changed something with their authentication and the class no longer worked. I felt like having this functionality again so I updated the API to work with Google's authentication changes, and also added a few things.

_logIn() now works.
getNewVoicemail() had to be edited slightly.
getReadSMS() was added to return read SMS messages.
getReadVoicemail() was added to return read voicemails.
markMessageUnread() was added to mark an SMS or voicemail as read.
getNewSMS() renamed to getUnreadSMS() for sake of Google's naming conventions.
getNewVoicemail() renamed to getUnreadVoicemail() for sake of Google's naming conventions.
markSMSRead() renamed to markMessageRead() for sake of Google's naming conventions.

I've tested all functionality completely, and the class is back to working condition. I know quite a few people online used this class at one point, hope you're willing to pull my changes.

-- Rhodey