Make project class-based #76

Summary

Currently op-js uses a singleton approach, where every family of commands is exported. This is nice and handy for quick importing, but we've had requests to make the project class-based so you can have multiple instances going at the same time.

Use cases

There are handful of benefits:

• Requiring different versions of the CLI
• Supplying a specific path to the op binary
• Supporting Service Account and Connect environment variables

Proposed solution

Convert all the exported command functions/objects into methods on an OPJS class that can be instantiated with options:

new OPJS({
  binaryPath: string;
  requiredVersion: string | SemVer;
  ...etc
});

Is there a workaround to accomplish this today?

All of this is technically possible with our current setup, but it's a little messy and obviously only supports a single instance of the library.