Support ORDER BY, GROUP BY, DISTINCT, and LIMIT in parser

In this PR:
- `parser` now uses a uniform export syntax, while retaining 'use strict'.
- Support for the following features added:
  - SELECT DISTINCT
  - ORDER BY (without directionaily)
  - GROUP BY
  - LIMIT
- added `test/parser.spec.js` Mocha tests with 100% parser coverage
- removed ancient `test/parser.js` with NodeUnit tests