* Update docs and changelog for URI, RFC822Name, and DNSName

As of 2.1 we want users to pass A-label strings, but we still accept
U-label strings and auto-encode on their behalf (with a deprecation
warning). However, we do not return U-label in the value attribute so
we are making a backwards incompatible change for users that utilize
internationalized domain names.

* language updates

* add presentational to the word list

* the linux dictionary is pathetic

* Backwards incompatible change to DNSName

During this release cycle we decided to officially deprecate passing
U-labels to our GeneralName constructors. At first we tried changing
this in a purely backwards compatible way but get_values_for_type made
that untenable. This PR modifies DNSName to take three different types.
U-label strings (which raises a deprecation warning), A-label strings
(the new preferred type), and bytes (which are assumed to be decodable
to unicode strings). The latter, while supported, is primarily intended
for use by our parser and allows us to return the actual encoded data in
a certificate even if it has not been properly encoded to A-label before
the certificate is created. (Of course, if the certificate contains
invalid utf8 sequences this will still fail, but let's handle one
catastrophic failure at a time).

* coverage

* don't delete that asterisk from a test. it does things.

* no bytes in DNSName. Private constructor for bypassing validation

* test unicode in dnsname (yuck)

* fix docs

* empty commit, you disappoint me codecov

* CI is the worst

* update security docs to indicate we staticaly link openssl there too

* spelling

This makes it so we don't have to pin sphinx while we wait for
sphinxcontrib-spelling to properly handle smart quotes

* Add support for AES XTS

We drop the non-byte aligned test vectors because according to NIST
http://csrc.nist.gov/groups/STM/cavp/documents/aes/XTSVS.pdf
"An implementation may support a data unit length that is not a
multiple of 8 bits." OpenSSL does not support this, so we can't
use those test vectors.

* fix docs and pep8

* docs fix

* the spellchecker is so frustrating

* add note about AES 192 for XTS (it's not supported)

* docs work

* enforce key length on ECB mode in AES as well (thanks XTS)

* a few more words about why we exclude some test vectors for XTS

* Declare that 2.1 is the last version to support Python 2.6

* It's the Final Countdown!

* add ChaCha20 support

* review feedback

* 256 divided by 8 is what again?

* ...