Fixes https://github.com/janl/mustache.js/issues/429

In an effort of ensuring consistent code style in test files as with
the "production" source code, we should run eslint as part of the
`$ npm test` script as well.

Most of the related fixes was done by `eslint` using the `--fix` argument.

Only special configuration tweaks for tests compared to the other
source code, is to allow functions declaration without names. The
rationale for allowing that in tests, is that the important reason we
have them in the source code (proper stacktraces) aren't as important
in test files.

* prevent value from being returned by Context.prototype.lookup if lookupHit is false

* add test for renderability of Array.length via dot notation

* Remove `typeof obj === 'object'` constraint in prop lookup

Allows rendering properties of primitive types that are not objects, such as a string.

* pop lookup needs to use hasOwnProperty for non-objs

* re-add  constraint in prop lookup, but make property lookups for primitives possible through dot notation

* add test to address #589 specifically

* enhance readability of primitiveHasOwnProperty and add comments to explain why it is used in one case but not the other

It was not being asserted anywhere else, and I was suspecting that
PR #552 was changing current (and correct) behaviour.

Either vim or git was going crazy with the indentation when I tried
improving the test via changing one of the lines, so I linted it all
together.

This closes a couple of potential exploit scenarios.
Backtick (`) for older IEs and equals (=) for unquoted attributes.

Refs 83b8e846a3
Closes https://github.com/janl/mustache.js/pull/388

Fixes #445

Fixes #442

+ minor fix for better error message when running specific render test

Fixes #415

CLI used to render a mustache template with a data view, writes the template into stdout when successfull. Otherwise meaningfull errors into stderr.

Fixes #424

Fixes #321

Fixes #322
Fixes #330
Fixes #331
Fixes #334

Issue: If I create a Mustache lambda to return numbers and I expect 0 to be of
those numbers, I'll instead only receive an empty string for 0 because it
evaluates to falsy.

Fix: Check the result of the lambda to be undefined or null. Only then should
it return the empty string.

Fixes #187

Fixes #186

Fixes #42

Also fixed a bug that occurs when using the triple-stache with a key
that contains a closing stache. Fixes #192.

- Cleaner separation of responsibilities in the code between
  scanning, parsing, compiling, and rendering functions.
- Much faster