Add htmlescape

[bouzuya]

Please fill in this template.

• Make your PR against the master branch.
• 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.)
• Follow the advice from the readme.
• Avoid common mistakes.
• Run tsc without errors.
• Run npm run lint package-name if a tslint.json is present.

Select one of these and delete the others:

If adding a new definition:

• The package does not provide its own types, and you can not add them.
• If this is for an NPM package, match the name. If not, do not conflict with the name of an NPM package.
• Create it with npm run new-package package-name, not by basing it on an existing project.
• tslint.json should be present, and tsconfig.json should have noImplicitAny, noImplicitThis, and strictNullChecks set to true.

[dt-bot]

htmlescape/index.d.ts

Checklist

• is correct naming convention?
  • https://www.npmjs.com/package/htmlescape - https://github.com/zertosh/htmlescape
• has a test file? (htmlescape-tests.ts or htmlescape-tests.tsx)
• pass the Travis CI test?