v1.0.0-rc.1

This is the first release candidate for zap's stable release. There are multiple breaking changes and improvements from the pre-release version. Most notably:

• Zap's import path is now "go.uber.org/zap" — all users will need to update their code.
• User-facing types and functions remain in the zap package. Code relevant largely to extension authors is now in the zapcore package.
• The zapcore.Core type makes it easy for third-party packages to use zap's internals but provide a different user-facing API.
• Logger is now a concrete type instead of an interface.
• A less verbose (though slower) logging API is included by default.
• Package-global loggers L and S are included.
• A human-friendly console encoder is included.
• A declarative config struct allows common logger configurations to be managed as configuration instead of code.
• Sampling is more accurate, and doesn't depend on the standard library's shared timer heap.