This comment ensures that the lexer is not stuck on zero-length tokens, in raw-blocks like {{{{a}}}} {{{{/a}}}}

In 4.4.4 the block-contents was matched with an eager match, which means
that with multiple raw-blocks of the same kind, the block was spanned
over the first ending-tag until the last one.
This commit replaces this by a non-eager match.

closes #1579

fixes #1548

- add a guard to show readable syntax error for if / unless helper
- prevents against 3 different errors that can be generated by different systax errors

The use of arrays was incorrect for the data type and causing problems when hash keys conflicted with array behaviors.

Fixes #1194

(cherry picked from commit 768ddbd)

When authoring tooling that parses Handlebars files and emits Handlebars
files, you often want to preserve the **exact** formatting of the input.
The changes in this commit add a new method to the `Handlebars`
namespace: `parseWithoutProcessing`. Unlike, `Handlebars.parse` (which
will mutate the parsed AST to apply whitespace control) this method will
parse the template and return it directly (**without** processing
😉).

For example, parsing the following template:

```hbs
 {{#foo}}
   {{~bar~}} {{baz~}}
 {{/foo}}
```

Using `Handlebars.parse`, the AST returned would have truncated the
following whitespace:

* The whitespace prior to the `{{#foo}}`
* The newline following `{{#foo}}`
* The leading whitespace before `{{~bar~}}`
* The whitespace between `{{~bar~}}` and `{{baz~}}`
* The newline after `{{baz~}}`
* The whitespace prior to the `{{/foo}}`

When `Handlebars.parse` is used from  `Handlebars.precompile` or
`Handlebars.compile`, this whitespace stripping is **very** important
(these behaviors are intentional, and generally lead to better rendered
output).

When the same template is parsed with
`Handlebars.parseWithoutProcessing` none of those modifications to the
AST are made. This enables "codemod tooling" (e.g. `prettier` and
`ember-template-recast`) to preserve the **exact** initial formatting.
Prior to these changes, those tools would have to _manually_ reconstruct
the whitespace that is lost prior to emitting source.

* Convert Exception to a class
* Add node param type declaration
* Test the types

…1586)

* Resolve eslint deprecation warning

  There was a DeprecationWarning message from eslint saying that `ecmaFeatures` property has 
  been deprecated.
  Moved it under the `parserOptions` as per recommended here - 
  https://eslint.org/docs/user-guide/migrating-to-2.0.0.
* Set escmaVersion = 6
* Use ES6 built-in global variables
* Remove flags in favor of ecmaVersion

- tests are not compiled with babel and must thus be in
  es5
- we don't use polyfills, so we need to make sure no
  functions aren't used that are not supported by popular browsers. (like Object.assign in Safari and IE11)
- Boths are errors that usually only appear when running
  tests in SauceLabs, which happens only on _after_
  merging a PR.