refactor: get rid of coffeescript

[dbushong]

• port src/assertive.coffee to readable lib/assertive.js
• port test/*.test.coffee to js
• remove coffee dependencies & mocha linkage
• remove build step
• update README.md
• install working eslint modules & rules

[aaarichter]

there is an error being thrown when running test-client with node 6.x

not ok 1 PhantomJS 2.1 - Global error: SyntaxError: Unexpected token 'const' at http://localhost:7357/test/tmp/test-bundle.js, line 1310
    ---
        Log: |
            { type: 'error',
              text: 'SyntaxError: Unexpected token \'const\' at http://localhost:7357/test/tmp/test-bundle.js, line 1310\n' }
    ...

test-bundle.js:

},{}],16:[function(require,module,exports){
(function (process){
'use strict';

/*
...
*/

// eat _ off the global scope, or require it ourselves if missing
// eslint-disable-next-line no-new-func
const global = Function('return this')();
let assert;

// eslint-disable-next-line global-require
const _ = global._ || require('lodash');
...

[dbushong]

D'oh. OK, pin the old version for the moment - I guess we'll use babel ;;

[dbushong]

@aaarichter should be fix as of https://github.com/groupon/assertive/pull/31 - will ship in a sec

[aaarichter]

Hey David - no problem. A hint to use babel should do it too 😉

We will add babel to our js asset pipeline