Add address base class
Add comparison methods to `Address` instance
Add proxy descriptor

Uses to transparently converts value to given type.
Unify interface for `from_addr` and `reply_to` addresses
Use class to wrap mail test suite
Better docstring for `Address` class
Add base class for address list
Unify interface for address lists, e.g. `cc`, `bcc`
Rename mail recipient list from `to_addrs` to `to`
To header contains only direct addressees
Exclude Bcc header from mail message for security reason

See http://tools.ietf.org/html/rfc2822 for details.
Sanitize email address into RFC 2822-compliant string
Strip newlines from formatted address
Address is truly when value is truly

Now possible to use address in conditional statements:

```python
if mail.reply_to:
    # Do something only when reply address is set
```
To, Cc and Bcc are empty lists if value is none
Bump version to 0.2.0

Use semantic version number.
Merge pull request #3 from vitalk/better-mail-api

Better mail api.