[#117] Replaced Make with gulp

[LarryBattle]

Replaced Make with gulp. The following build options are now available.

• npm run build - uses browserify to consolidate all js files in ./lib and creates a numbers.js and numbers.min.js in ./src.
• npm run format - uses jsbeautifier to format all js files in ./lib and ./test
• npm run lint - run jshint against code in ./lib and ./test
• npm run test - run test cases in ./test using mocha.

Reference: https://github.com/sjkaliski/numbers.js/issues/117