Also upgraded to `@definitelytyped/dtslint`.

Extracts the parser to `@handlebars/parser`, where it can be shared
between different implementations. This means that e.g. Glimmer/Ember
will be able to iterate on new features without forcing Handlebars to
adopt them immediately, and vice versa. All implementors will be able to
absorb changes as it makes sense for them.

- some indirect dependencies install @types packages which are not compatible with the older typescript.
- adjusted test's tsconfig to not pick these up automatically, as the actual .d.ts does not depend on these external types.

This commmit adds the runtime options
- `allowProtoPropertiesByDefault` (boolean, default: false) and
- `allowProtoMethodsByDefault` (boolean, default: false)`
which can be used to allow access to prototype properties and
functions in general.

Specific properties and methods can still be disabled from access
via `allowedProtoProperties` and `allowedProtoMethods` by
setting the corresponding values to false.

The methods `constructor`, `__defineGetter__`, `__defineSetter__`, `__lookupGetter__`
and the property `__proto__` will be disabled, even if the allow...ByDefault-options
are set to true. In order to allow access to those properties and methods, they have
to be explicitly set to true in the 'allowedProto...'-options.

A warning is logged when the a proto-access it attempted and denied
by default (i.e. if no option is set by the user to make the access
decision explicit)

Disallow access to prototype properties and methods by default.
Access to properties is always checked via
`Object.prototype.hasOwnProperty.call(parent, propertyName)`.

New runtime options:
- **allowedProtoMethods**: a string-to-boolean map of property-names that are allowed if they are methods of the parent object.
- **allowedProtoProperties**: a string-to-boolean map of property-names that are allowed if they are properties but not methods of the parent object.

```js
const template = handlebars.compile('{{aString.trim}}')
const result = template({ aString: '  abc  ' })
// result is empty, because trim is defined at String prototype
```

```js
const template = handlebars.compile('{{aString.trim}}')
const result = template({ aString: '  abc  ' }, {
  allowedProtoMethods: {
    trim: true
  }
})
// result = 'abc'
```

Implementation details: The method now "container.lookupProperty"
handles the prototype-checks and the white-lists. It is used in
- JavaScriptCompiler#nameLookup
- The "lookup"-helper (passed to all helpers as "options.lookupProperty")
- The "lookup" function at the container, which is used for recursive lookups in "compat" mode

Compatibility:
- **Old precompiled templates work with new runtimes**: The "options.lookupPropery"-function is passed to the helper by a wrapper, not by the compiled templated.
- **New templates work with old runtimes**: The template contains a function that is used as fallback if the "lookupProperty"-function cannot be found at the container. However, the runtime-options "allowedProtoProperties" and "allowedProtoMethods" only work with the newest runtime.

BREAKING CHANGE:
- access to prototype properties is forbidden completely by default

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

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.

closes #1558

- derived from the object structure seen in the debugger

closes #1534

- Handlebars.VM is actually not part of the API,
  but Handlebars.VM.resolvePartial is mentioned
  in the documentation and is thus now treated
  as part of the API.

Closes #1534

- Add support for custom helpers while keeping
  the list of builtin-helpers to maintain for
  autocompletion support

closes #1544

- Move typings from lib/ to types/.
- Add dtslint for validating types.
- Use grunt-bg-shell to call out to dtslint during build step.