update google/apiclient-servies to v0.9 (googleapis#1128)

removes errant symlinks

removes stash logic, adds caching test for MemoryCache (googleapis#1085)

updates google/apiclient-services to 0.7 (googleapis#1053)

Fix incorrect function call in UPGRADING.md (googleapis#996)

adds service account, OAuth, general usage, and proxying to README (g…

…oogleapis#972)

Update README for v2.0 stable release (googleapis#968)

fixes branch alias for dev v1-master

adds PSR-6 and removes custom caching (googleapis#943)

* adds PSR-6 and removes custom caching

* Adds callback

* documents these changes in the README

Merge pull request googleapis#895 from bshaffer/issue-894

passes in cache to token verifier by default