Refactor public api

[dinoboff]

Add targaryen.database(rules, data, now)

This is the public facing API:

• targaryen.database(rules: object|Ruleset, data: object|DataNode, now: null|number): Database;
• Database.as(auth: null|object): Database;
• Database.read(path: string, now: null|number): Result;
• Database.write(path: string, value: any, priority: any, now: null|number): Result;
• Database.update(path: string, patch: object, now: null|number): Result.

Example:

const assert = require('assert');
const targaryen = require('targaryen');

const rules = {
  rules: {
    foo: {
      '.write': 'true'
    }
  }
};
const data = {foo: 1};
const auth = {uid: 'someuid'};

const database = targaryen.database(rules, data);
const {allowed, newDatabase, info} = database.as(auth).write('/foo', 2);

console.log('Rule evaluations:\n', info);
assert.ok(allowed);

assert.equal(newDatabase.rules, database.rules);
assert.equal(newDatabase.root.foo.$value(), 2);
assert.equal(newDatabase.auth, auth);

targaryen also provides targaryen.util to help write testing framework plugin.

Result main properties are path, newValue, auth, database and newDatabase.

Low level constructors (Ruleset and DataSnapshot) or functions (like pathMerger) are not accessible directly anymore.