* begin security bindings
* secure channel creation
* SSL credentials support
* add client-side ssl support
* ssl test
* read file before passing to channel credentials, free credentials when done creating
* use localhost key/cert for test
* WIP sketch of callbacks for metadata plugins
* conversion from Haskell auth processor to C
* add test for custom server metadata auth processor
* wip auth failure test
* rebase tweak
* working test of custom auth metadata server processor
* improve security docs, clean up
* add unsafe layer client-side auth metadata plugin functionality
* add client config option for custom auth metadata
* WIP client-side metadata auth plugin. Crashing when calling C callback.
* get initial version of client-side metadata plugins working
* replace String with ByteString in a few places, add function for getting AuthProperty
* AuthContext utilities and more documentation
* end-to-end test of client and server auth plugins
* remove redundant tests
* function for parents in unary calls, add deactivated failing test for auth metadata propagation from parent to child
* some cleanup
* tweaks
* more tweaks
* remove unused file
* docs tweak
* consolidate exports
* update protobuf-wire commit
