explicit export types

[alverdal]

Explicit export of api types to allow for a more flexible use of rule definitions and this library.
Currently, only RuleEngine is exported in the dist/index.d.ts but it would be nice to have the other types exported as well.

For instance, to be able to define rules as re-useable functions and defining rules as separate variable.

const rules: Rule[] = [
   myReuseableFunction(api, fact)
  ,{
    name: 'ageOfDog',
    priority: 1,
    condition: (api: API, fact: Fact) => {
      api.when(fact.age > 5)
    },
    consequence: (R: API, fact: Fact) => {
      fact.result = false
      fact.reason = 'The dog is older than 5 years.'
      R.stop()
    }
  }
]

eng.register(rules)

[miccheng]

@mithunsatheesh Would you want to merge this in?

[mithunsatheesh]

done

[mithunsatheesh]

closes #143

[mithunsatheesh]

closes #142

[miccheng]

Thanks for doing this! And releasing a new version. Really helped reduce the TypeScript issues.