Begins forcing access to the RPC through an object

[tjayrush]

We're going to make all access to the RPC go through an object (maybe called the Provider?) This will have a lot of benefits:

1. We can initialize that object in options.go, so that by the time to execution gets to Validate and then the Handlers, we know we have a connection,
2. We can make the RPC connection a field on the opts structures for each tool. In this way, we no longer have to pass it around through the function interfaces. This makes the code much easier to read. This has the benefit that every handler automatically has caching which was not true previously, for example.
3. We can add features in the future such as rate limiting and/or API keys
4. We remove the "danger" of having an nil rpcOptions object which was creeping into the code.
5. The documentation is MUCH easier to read.