The `AuthorityKeyIdentifier.authority_cert_issuer` docs state that it returns a `Name` instance, but it [actually returns a list of `GeneralName` instances or `None`](https://github.com/pyca/cryptography/blob/master/src/cryptography/x509/extensions.py#L157).

* switch to py3 on docs job

* somehow unicode isn't a word

* 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

* add freshest CRL support

* add tests

* add changelog

* add tests for FreshestCRL generation

This is an extension for CRLs

* add support for the TLSFeature extension in x509

This extension is used for OCSP Must-Staple.

* fix changelog link

* pep8

* refactor to support the sequence properly and add status_request_v2

* update some language

* add test vector, implement eq/ne/hash on TLSFeature

* address review comments

* add changelog and a warning

* document this properly