Go-SDK - v1.0.0-rc1

## [1.0.0-rc1] - December 4th, 2019

## New Features
- feat(PollingConfigManager): Implemented caching headers in PollingConfigManager. [#189](https://github.com/optimizely/go-sdk/pull/189)
- feat(api): Add top-level wrapper for more convenient usage. [#191](https://github.com/optimizely/go-sdk/pull/191)

### Bug Fixes
- fix(audience-evaluation): Fixed null-bubbling issues. [#177](https://github.com/optimizely/go-sdk/pull/177)
- fix: correct error returned when SDK key is invalid [#203](https://github.com/optimizely/go-sdk/pull/203)
- fix: Invalid datafile JSON should return an error [#205](https://github.com/optimizely/go-sdk/pull/205)

https://github.com/optimizely/go-sdk/releases/tag/v1.0.0-rc1