Add a coherent unit test framework

[dmitrizagidulin]

Re-adding @dan-f's PR #156, which seems to have gone missing in master (stray push -f?).

[dmitrizagidulin]

In testing this branch, I did an npm install followed by npm test. This is the error I got:

$ npm test

> [email protected] test /Users/dmitri/code/_Solid/rdflib.js
> npm run test:unit && make test

> [email protected] test:unit /Users/dmitri/code/_Solid/rdflib.js
> mocha --growl --require babel-register tests/unit/**-test.js

module.js:440
    throw err;
    ^
Error: Cannot find module 'diff'
    at Function.Module._resolveFilename (module.js:438:15)
    at Function.Module._load (module.js:386:25)
    at Module.require (module.js:466:17)
    at require (internal/module.js:20:19)
    at Object.<anonymous> (/Users/dmitri/code/_Solid/rdflib.js/node_modules/mocha/lib/reporters/base.js:8:12)
    at Module._compile (module.js:541:32)
    at Object.Module._extensions..js (module.js:550:10)
    at Module.load (module.js:456:32)
    at tryModuleLoad (module.js:415:12)
    at Function.Module._load (module.js:407:3)

Am I missing anything obvious?

[dmitrizagidulin]

Never mind, was a one-off issue due to an npm linked lib. Sorted it out, npm test runs smoothly now. Merging.