C++ shared library is published to a Maven repository

@adammurdoch commented on [Mon May 22 2017](https://github.com/gradle/stable-native/issues/21)

Take the output of #17 and publish it as a Maven module in a Maven repository.

- Publish the Zipped public headers of the library, plus the link, runtime and debug files.
- Generate a POM that defines the compile and runtime dependencies.
- Generate a Gradle meta-data file that describes the library.
- Support either the `maven-publish` plugin or `maven` plugin but not both.

Out-of-scope for this story:

- Publish multiple variants of a C++ library.
- Ivy support.
- Header only or windows resources only libraries.

Start by reviewing the output of #17 and how this project currently handles native library publication. Define the Maven module contents, POM dependencies, and Gradle metadata required by the issue, then verify that publication works with either the maven-publish or maven plugin, but not both.

Written by the indexing model from the issue text.