PMMail and PMBounceManager objects for Postmark (http://postmarkapp.com)

PYTHON INFORMATION:
    Works on Python 2.4 and better.  Versions
    2.4 and 2.5 will require the "simplejson" 
    library from http://code.google.com/p/simplejson/
    Python 2.6 has JSON support built in.

CHANGE LOG:
    Version 0.2.0
        - Merged with frozenskys/master to bring in PMBounceManager
        - Support for multiple to/cc (limit: 20 per)
        - Changed .recipient to .to (legacy support for .recipient left in)
        - Tag support (.tag) added
        - Fixed the email endpoint
        - Fixed a Django backend issue for multiple recipients (max 20)

    Version 0.1.6
        - Added a new PMBounceManager Class that allows easy access to the PostMark
          bounce API.
        
    Version 0.1.5
        - Added ".cc" property for carbon copy recipients. Changed django_backend to 
          support multiple recipients, and to use "to" rather than "recipients" on the django
          mail object to prevent accidental leakage of BCC recipients.
          
    Version 0.1.4
        - Added ".reply_to" property.  The "ReplyTo" custom header is unallowed by Postmark 
          now, and their documentation has been updated to reflect the change.
          http://developer.postmarkapp.com

    Version 0.1.3
        - Major fix to the way properties were being used, fixes doc strings in properties
        - "custom_headers" is now always a dict, even if set to None

    Version 0.1.2
        - Added 'custom_headers' property (must be a dictionary) to PMMail object
        - Added optional 'test' argument to send function to print JSON message instead of actually sending it
        
    Version 0.1.1:
        - Initial release

USAGE:
    Make sure you have a Postmark account.  Visit
    http://postmarkapp.com to sign up for an account.
    Requires a Postmark API key.

    Import postmark.PMMail to use Postmark.  Check
    class documentation on PMMail object for more 
    information.
    
DJANGO:
    The library can be used stand-alone with Django.  You can also
    add the settings:
    
    POSTMARK_API_KEY    = 'your-key'
    POSTMARK_SENDER     = 'sender@signature.com'
    
    to your settings.py file, and when you create a new PMMail object,
    it will grab the API key and sender automatically.  Make sure the 
    sender email address is one of your Sender Signature email addresses
    in Postmark. You can also customize the name on the sender by 
    changing the format from 'email@address.com' to 
    'Sender Name <email@address.com>' as long as the email part is 
    part of a Sender Signature in Postmark

    To reoute all Django E-Mail functions like send_mail() and
    mail_admins() through postmark use the following setting:

    EMAIL_BACKEND = 'postmark.django_backend.EmailBackend'

    But keep in mind that even when using standard Django functions
    the sender must be registered with postmarkapp.com.
    

EXCEPTIONS:
    PMMailMissingValueException(Exception):
        One of the required values for attempting a send request is missing

    PMMailSendException(Exception):
        Base Postmark send exception

    PMMailUnauthorizedException(PMMailSendException):
        401: Unathorized sending due to bad API key

    PMMailUnprocessableEntityException(PMMailSendException):
        422: Unprocessable Entity - usually an exception with either the sender
        not having a matching Sender Signature in Postmark.  Read the message
        details for further information

    PMMailServerErrorException(PMMailSendException):
        500: Internal error - this is on the Postmark server side.  Errors are
        logged and recorded at Postmark.

    PMMailURLException(PMMailSendException):
        A URLError was caught - usually has to do with connectivity
        and the ability to reach the server.  The inner_exception will
        have the base URLError object.
        
TODO: 
    Add automatic multipart emails via regex stripping of HTML tags from html_body
    if the .multipart property is set to True
    Refactor PMBounceManager Object and improve error handling within it.
    Add PMBounceManager example to the Django test.