With the creation of the [metamask-extension-provider](https://github.com/MetaMask/metamask-extension-provider) we have our first non-core module that is dependent on the inpage-provider and port-stream. To reduce the size of its dependencies, I have moved the [metamask-inpage-provider](https://github.com/MetaMask/metamask-inpage-provider) into its own module, as well as [extension-port-stream](https://github.com/MetaMask/extension-port-stream). This allows them to be more easily depended & iterated on by external projects.