Python 2.4, 2.5, 2.6, 3.2 and 3.3 are end of life. They are no longer
receiving bug fixes, including for security issues. These Pythons went
EOL on:

Python 2.6: 2013-10-29
Python 3.2: 2016-02-20
Python 3.3: 2017-09-29

For additional details on supported Python versions, see:

https://devguide.python.org/#status-of-python-branches

Removing support for EOL Pythons will reduce testing and maintenance
resources.

Using pypinfo, here are the download statistics of the project for the
last 30 days, showing limited downloads from EOL Pythons:

| python_version | percent | download_count |
| -------------- | ------: | -------------: |
| 2.7            |  90.33% |      7,975,885 |
| 3.6            |   4.95% |        437,261 |
| 3.5            |   2.99% |        263,637 |
| 3.4            |   1.02% |         89,723 |
| 2.6            |   0.69% |         60,511 |
| 3.7            |   0.02% |          2,024 |
| 3.3            |   0.00% |            441 |
| 3.2            |   0.00% |             38 |
| 3.8            |   0.00% |              9 |
| None           |   0.00% |              2 |

By removing support for older Pythons, can remove or update the
following workarounds and code:

* Built-in function bin() is always available.
* Built-in function callable() is always available.
* Built-in function all() is always available.
* The collections.OrderedDict class is always available.
* The datetime.strptime() method is always available.
* The platform module is always available.
* The string.partition() method is always available.
* The NullHandler class is always available.
* The method .__trunc__() is always available.
* Can use set literals.
* Updated unittest is always available. The unittest2 module is
  unnecessary.

Users on older versions of Python can continue to download, install, and
use older versions of the library that continue to have support for
older Pythons.

The goal of this change is to make the decoder stopping on input
data starvation and resuming from where it stopped whenever the
caller decides to try again (hopefully making sure that some more
input becomes available).

This change makes it possible for the decoder to operate on streams
of data (meaning that the entire DER blob might not be immediately
available on input).

On top of that, the decoder yields partially reconstructed ASN.1
object on input starvation making it possible for the caller to
inspect what has been decoded so far and possibly consume partial
ASN.1 data.

All these new feature are natively available through
`StreamingDecoder` class. Previously published API is implemented
as a thin wrapper on top of that ensuring backward compatibility.

* Fix CER/DER encoders to respect open types

Added a bunch of unit tests to CER/DER codecs covering open types.

Also extend copyright to the year 2019

Also fixed a couple of crashes in debug messages