add support for update_into on CipherContext (#3190)
* add support for update_into on CipherContext
This allows you to provide your own buffer (like recv_into) to improve
performance when repeatedly calling encrypt/decrypt on large payloads.
* another skip_if
* more skip_if complexity
* maybe do this right
* correct number of args
* coverage for the coverage gods
* add a cffi minimum test tox target and travis builder
This tests against macOS so we capture some commoncrypto branches
* extra arg
* need to actually install py35
* fix
* coverage for GCM decrypt in CC
* no longer relevant
* 1.8 now
* pep8
* dramatically simplify
* update docs
* remove unneeded test
* changelog entry
* test improvements
* coverage fix
* add some comments to example
* move the comments to their own line
* fix and move comment
9 files changed