* Replace legacy file handling with a context manager.

* flake8 fix

Co-authored-by: Alex Gaynor <alex.gaynor@gmail.com>

* drop python 3.4 support

Our dependencies have started dropping support so it is becoming
difficult to test. Additionally, Python 3.4 represents <2% of our
downloads, so taking on a large maintenance burden to maintain support
isn't a good use of limited time. Accordingly, we're dropping testing
infrastructure and migrating our abi3 wheels to py35+.

* use removed instead of dropped

* add single_extensions to OCSPResponse (#4753)

* new vector, updateed docs, more stringent parser, changelog, etc

* simplify PR (no SCT for now)

* add a comment

* finish pulling out the sct stuff so tests might actually run

* Support ed25519 in csr/crl creation

* Tests for ed25519/x509

* Support ed448 in crt/csr/crl creation

* Tests for ed448/x509

* Support ed25519/ed448 in OCSPResponseBuilder

* Tests for eddsa in OCSPResponseBuilder

* Builder check missing in create_x509_csr

* Documentation update for ed25519+ed448 in x509

* fix coverage by adding two artificial DSA public keys

One key removes the optional parameters from the structure to cover a
branch conditional, and the other key has its BITSTRING padding value
set to a non-zero value.

* lexicographic? never heard of it