Add typescript typings

[stretchkennedy]

Summary

Adds typescript typings. This will allow typescript users to use random-words with no extra effort.

What are the specific steps to test this change?

• Find a typescript project scaffold somewhere
• Run yarn add 'git+https://github.com/stretchkennedy/random-words.git#upstream-ts-declarations'
• See if you can import and use random-words

What kind of change does this PR introduce?

(Check at least one)

• Bug fix
• New feature
• Refactor
• Documentation
• Build-related changes
• Other

Make sure the PR fulfills these requirements:

• It includes a) the existing issue ID being resolved, b) a convincing reason for adding this feature, or c) a clear description of the bug it resolves
• The changelog is updated
• Related documentation has been updated
• Related tests have been updated

Other information:

Adapted from work I did in my nodejs fork. I'm putting it here in case it's useful to anyone else. See #7 for prior work, though this PR uses a separate function declaration for options that set join to avoid a return type of string | string[].

I don't think it needs documentation and I don't think tests would be useful for typescript typings (but I'm happy to write both if a maintainer can point me in the right direction).

[juicycool92]

looks good to me, and seems like its commit to master branch.
when will this module update on npm?
im expecting to use it when it start support ts

[boutell]

This has just been published to npm. Thanks to @stretchkennedy