Remove Python 2 compatibility code (#188)

* Remove Python 2 compatibility code

- Remove from __future__ imports from all files
- Simplify emails/compat: remove Python 2 branch, keep only Python 3 code
- Delete unused ordereddict.py and orderedset.py
- Remove is_py2/is_py3/is_py26/is_py34_plus version checks
- Remove Travis CI pypy workaround from test_loaders
- All 74 tests pass on Python 3.14

* Remove emails.compat module entirely

Move to_unicode, to_native, to_bytes, formataddr to emails.utils.
Replace all compat aliases with direct stdlib imports:
- string_types -> str
- text_type -> str
- is_callable -> callable()
- urlparse -> urllib.parse
- NativeStringIO/StringIO/BytesIO -> io
- OrderedDict -> collections

Author: lavr

emails/__init__.py

@@ -35,7 +35,6 @@
 
 """
 
-from __future__ import unicode_literals
 
 __title__ = 'emails'
 __version__ = '0.6'

emails/backend/inmemory/__init__.py

@@ -1,5 +1,4 @@
 # encoding: utf-8
-from __future__ import unicode_literals
 
 __all__ = ['InMemoryBackend', ]
 

emails/backend/smtp/backend.py

@@ -1,5 +1,4 @@
 # encoding: utf-8
-from __future__ import unicode_literals
 import smtplib
 import logging
 from functools import wraps

emails/backend/smtp/exceptions.py

@@ -1,5 +1,4 @@
 # encoding: utf-8
-from __future__ import unicode_literals
 import socket