Composer.json, twiddler methods, bug fixes

Hiya, I added a few features to your handy library! It now has a composer.json file so that I can use composer to configure it as a dependency. I also added support for the process control RPC methods added by the [twiddler extension](https://github.com/mnaberez/supervisor_twiddler). 

Also, I added some standard RPC methods that were missing (most likely because they're also missing from the official API documentation!) and fixed a problem where the general-purpose RPC calls (i.e. listMethods) were being accessed under the wrong namespace.

I'm also wondering if you'd like to add your library to packagist to make it that much easier to use?