Update typings for handlebars: Add options param to parse

[timlindvall]

• Add optional options param to parse. This reflects the options param
  in the Handlebars source code. Also defines interface ParseOptions,
  which includes the options that have an effect on Handlebars parsing.
• Fix duplicate properties in tsconfig.json.
• Fix typo in import in handlebars-tests.ts.

Reference Source:
https://github.com/wycats/handlebars.js/blob/master/lib/handlebars/compiler/base.js#L11

Non-breaking change (new param is optional).

---

• Use a meaningful title for the pull request. Include the name of the package modified.
• Test the change in your own code. (Compile and run.)
  • Tested by patching modified types into glimmer-vm.
• Add or edit tests to reflect the change. (Run with npm test.)
• Follow the advice from the readme.
• Avoid common mistakes.
• Run npm run lint package-name (or tsc if no tslint.json is present).

If changing an existing definition:

• Provide a URL to documentation or source code which provides context for the suggested changes: https://github.com/wycats/handlebars.js/blob/master/lib/handlebars/compiler/base.js#L11
• Increase the version number in the header if appropriate.
  • N/A
• If you are making substantial changes, consider adding a tslint.json containing { "extends": "dtslint/dt.json" }.
  • N/A (Already present)

[typescript-bot]

@zimmi88 Thank you for submitting this PR!

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[typescript-bot]

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[stefanpenner]

LGTM

[sandersn]

This typo is good evidence that handlebars should switch to the new global syntax:

``ts
export = Handlebars;
export as namespace Handlebars;

[timlindvall]

Thanks for the feedback! In parallel, I've been working to have Handlebars provide its own typings as part of the package (handlebars-lang/handlebars.js#1487), so I'll look into making this change over there (likely in a follow-up PR).